Delete Ref & VectorRef and add GetDataSafely

[chenwhql]

This PR revome two invalid error check interface, and add a valid error check interface:

not change the code logic, only enhances the error message

RemoveRef & VectorRef check (remove safe_ref.h)

Ref & VectorRef are used to safely obtain the data pointed to by a pointer. Before * ptr, they will check whether the pointer is nullptr. but...

• The code used these two interface get data from ptr, almost no error messages
• use Ref & VectorRef cannot tell users the actual error pointer
• use Ref & VectorRef cannot tell users the actual error file & line number
• More than 100 places used

example:

int* a = nullptr;
paddle::operators::detail::Ref(a);

----------------------
Error Message Summary:
----------------------
Error:
[Hint: ptr should not be null.] at (/work/paddle/paddle/fluid/operators/detail/safe_ref.h:28)

• no error message!
• error ptr value name is a, not ptr!
• error file & line are enforce_test.cc:369, not safe_ref.h:28!

Add GET_DATA_SAFELY

• A new error check interface in enforce.h to replace Ref & VectorRef, resolve all above problems!
• You only need use GET_DATA_SAFELY macro, and pass in 3 key word, you can get a complete and accurate error message
• The error message using the new interface is like follows:

int* a = nullptr;
GET_DATA_SAFELY(a, "Input", "X", "dummy");

----------------------
Error Message Summary:
----------------------
InvalidArgumentError: Unable to get int data of Input X in operator dummy. Possible reasons are:
  1. The X is not the Input of operator dummy;
  2. The X has no corresponding variable passed in;
  3. The X corresponding variable is not initialized.
  [Hint: pointer a should not be null.] at (/work/paddle/paddle/fluid/platform/enforce_test.cc:383)

[raindrops2sea]

LGTM