[3.12] gh-115091: Remove a left-over sentence that refers to Py_OptimizeFlag from ctypes documentation (GH-115092) (GH-115936)

Remove a left-over sentence that refers to an example that was present in Python 3.10 and was using ``Py_OptimizeFlag``.
(cherry picked from commit 915d7dd090387b52f62bdc2f572413bc87297cee)

Co-authored-by: Antti Haapala <antti.haapala@interjektio.fi>