gh-101100: Remove roles of sample classes in howto/*

Removed sphinx roles of some classes and methods,
as the classes are defined in the sample codes, not in Python.

Fixed warnings:
```
howto/descriptor.rst:45: WARNING: py:class reference target not found: Ten [ref.class]
howto/descriptor.rst:218: WARNING: py:class reference target not found: Person [ref.class]
howto/descriptor.rst:218: WARNING: py:class reference target not found: Person [ref.class]
howto/descriptor.rst:256: WARNING: py:class reference target not found: Person [ref.class]
howto/descriptor.rst:340: WARNING: py:class reference target not found: Validator [ref.class]
howto/descriptor.rst:363: WARNING: py:class reference target not found: Validator [ref.class]
howto/descriptor.rst:363: WARNING: py:meth reference target not found: validate [ref.meth]
howto/descriptor.rst:372: WARNING: py:class reference target not found: OneOf [ref.class]
howto/descriptor.rst:374: WARNING: py:class reference target not found: Number [ref.class]
howto/descriptor.rst:378: WARNING: py:class reference target not found: String [ref.class]
howto/descriptor.rst:876: WARNING: py:class reference target not found: Field [ref.class]
howto/descriptor.rst:1143: WARNING: py:func reference target not found: Property [ref.func]
howto/descriptor.rst:1725: WARNING: py:class reference target not found: Object [ref.class]
howto/enum.rst:78: WARNING: py:class reference target not found: Weekday [ref.class]
howto/enum.rst:90: WARNING: py:class reference target not found: Weekday [ref.class]
howto/enum.rst:113: WARNING: py:class reference target not found: Weekday [ref.class]
howto/enum.rst:131: WARNING: py:class reference target not found: Weekday [ref.class]
howto/enum.rst:576: WARNING: py:class reference target not found: Animal [ref.class]
howto/enum.rst:893: WARNING: py:class reference target not found: FloatEnum [ref.class]
```

Doc/howto/descriptor.rst

@@ -42,7 +42,7 @@ add new capabilities one by one.
 Simple example: A descriptor that returns a constant
 ----------------------------------------------------
 
-The :class:`Ten` class is a descriptor whose :meth:`__get__` method always
+The ``Ten`` class is a descriptor whose :meth:`__get__` method always
 returns the constant ``10``:
 
 .. testcode::
@@ -215,8 +215,8 @@ Customized names
 When a class uses descriptors, it can inform each descriptor about which
 variable name was used.
 
-In this example, the :class:`Person` class has two descriptor instances,
-*name* and *age*.  When the :class:`Person` class is defined, it makes a
+In this example, the ``Person`` class has two descriptor instances,
+*name* and *age*.  When the ``Person`` class is defined, it makes a
 callback to :meth:`__set_name__` in *LoggedAccess* so that the field names can
 be recorded, giving each descriptor its own *public_name* and *private_name*:
 
@@ -253,7 +253,7 @@ be recorded, giving each descriptor its own *public_name* and *private_name*:
         def birthday(self):
             self.age += 1
 
-An interactive session shows that the :class:`Person` class has called
+An interactive session shows that the ``Person`` class has called
 :meth:`__set_name__` so that the field names would be recorded.  Here
 we call :func:`vars` to look up the descriptor without triggering it:
 
@@ -337,7 +337,7 @@ any data, it verifies that the new value meets various type and range
 restrictions.  If those restrictions aren't met, it raises an exception to
 prevent data corruption at its source.
 
-This :class:`Validator` class is both an :term:`abstract base class` and a
+This ``Validator`` class is both an :term:`abstract base class` and a
 managed attribute descriptor:
 
 .. testcode::
@@ -360,22 +360,22 @@ managed attribute descriptor:
         def validate(self, value):
             pass
 
-Custom validators need to inherit from :class:`Validator` and must supply a
-:meth:`validate` method to test various restrictions as needed.
+Custom validators need to inherit from ``Validator`` and must supply a
+``validate`` method to test various restrictions as needed.
 
 
 Custom validators
 -----------------
 
 Here are three practical data validation utilities:
 
-1) :class:`OneOf` verifies that a value is one of a restricted set of options.
+1) ``OneOf`` verifies that a value is one of a restricted set of options.
 
-2) :class:`Number` verifies that a value is either an :class:`int` or
+2) ``Number`` verifies that a value is either an :class:`int` or
    :class:`float`.  Optionally, it verifies that a value is between a given
    minimum or maximum.
 
-3) :class:`String` verifies that a value is a :class:`str`.  Optionally, it
+3) ``String`` verifies that a value is a :class:`str`.  Optionally, it
    validates a given minimum or maximum length.  It can validate a
    user-defined `predicate
    <https://en.wikipedia.org/wiki/Predicate_(mathematical_logic)>`_ as well.
@@ -873,7 +873,7 @@ care of lookups or updates:
             conn.execute(self.store, [value, obj.key])
             conn.commit()
 
-We can use the :class:`Field` class to define `models
+We can use the ``Field`` class to define `models
 <https://en.wikipedia.org/wiki/Database_model>`_ that describe the schema for
 each table in a database:
 
@@ -1140,7 +1140,7 @@ to wrap access to the value attribute in a property data descriptor:
             self.recalc()
             return self._value
 
-Either the built-in :func:`property` or our :func:`Property` equivalent would
+Either the built-in :func:`property` or our ``Property`` equivalent would
 work in this example.
 
 
@@ -1722,7 +1722,7 @@ Python:
                 )
             super().__delattr__(name)
 
-To use the simulation in a real class, just inherit from :class:`Object` and
+To use the simulation in a real class, just inherit from ``Object`` and
 set the :term:`metaclass` to :class:`Type`:
 
 .. testcode::

Doc/howto/enum.rst

@@ -79,15 +79,15 @@ Unlike many languages that treat enumerations solely as name/value pairs,
 Python Enums can have behavior added.  For example, :class:`datetime.date`
 has two methods for returning the weekday: :meth:`weekday` and :meth:`isoweekday`.
 The difference is that one of them counts from 0-6 and the other from 1-7.
-Rather than keep track of that ourselves we can add a method to the :class:`Weekday`
+Rather than keep track of that ourselves we can add a method to the ``Weekday``
 enum to extract the day from the :class:`date` instance and return the matching
 enum member::
 
         @classmethod
         def from_date(cls, date):
             return cls(date.isoweekday())
 
-The complete :class:`Weekday` enum now looks like this::
+The complete ``Weekday`` enum now looks like this::
 
     >>> class Weekday(Enum):
     ...     MONDAY = 1
@@ -110,7 +110,7 @@ Now we can find out what today is!  Observe::
 
 Of course, if you're reading this on some other day, you'll see that day instead.
 
-This :class:`Weekday` enum is great if our variable only needs one day, but
+This ``Weekday`` enum is great if our variable only needs one day, but
 what if we need several?  Maybe we're writing a function to plot chores during
 a week, and don't want to use a :class:`list` -- we could use a different type
 of :class:`Enum`::
@@ -128,7 +128,7 @@ of :class:`Enum`::
 We've changed two things: we're inherited from :class:`Flag`, and the values are
 all powers of 2.
 
-Just like the original :class:`Weekday` enum above, we can have a single selection::
+Just like the original ``Weekday`` enum above, we can have a single selection::
 
     >>> first_week_day = Weekday.MONDAY
     >>> first_week_day
@@ -580,7 +580,7 @@ values.  The last two options enable assigning arbitrary values to
 enumerations; the others auto-assign increasing integers starting with 1 (use
 the ``start`` parameter to specify a different starting value).  A
 new class derived from :class:`Enum` is returned.  In other words, the above
-assignment to :class:`Animal` is equivalent to::
+assignment to ``Animal`` is equivalent to::
 
     >>> class Animal(Enum):
     ...     ANT = 1
@@ -891,7 +891,7 @@ simple to implement independently::
         pass
 
 This demonstrates how similar derived enumerations can be defined; for example
-a :class:`FloatEnum` that mixes in :class:`float` instead of :class:`int`.
+a ``FloatEnum`` that mixes in :class:`float` instead of :class:`int`.
 
 Some rules: