[3.13] gh-149096: Remove 'im_*' attribute reference from inspect module docstring (GH-149108) (#149440)

gh-149096: Remove  'im_*' attribute reference from inspect module docstring (GH-149108)

The im_class/func/self names were removed in 3.0.  The prefix appears nowhere else in inspect.py
and nowhere in inspect.rst.
(cherry picked from commit e4444538dcd60a1b655c620b4d3bba59a7830f25)

Co-authored-by: Vineet Kumar <108144301+whyvineet@users.noreply.github.com>