Remove the duplicated docs for a BackendV1 classmethod (#12443)

(cherry picked from commit 16acb80)

qiskit/providers/backend.py

@@ -88,12 +88,6 @@ def __init__(self, configuration, provider=None, **fields):
             This next bit is necessary just because autosummary generally won't summarise private
             methods; changing that behaviour would have annoying knock-on effects through all the
             rest of the documentation, so instead we just hard-code the automethod directive.
-
-        In addition to the public abstract methods, subclasses should also implement the following
-        private methods:
-
-        .. automethod:: _default_options
-           :noindex:
         """
         self._configuration = configuration
         self._options = self._default_options()