[3.15] gh-152587: Stop documenting bogus default values in tkinter variable methods...

[3.15] gh-152587: Stop documenting bogus default values in tkinter variable methods (GH-152594) (GH-152596)

The name parameter of Misc.wait_variable(), setvar() and getvar() and the
value parameter of setvar() should not be optional.  Their default values
('PY_VAR' and '1') are not meaningful and should not be advertised.
(cherry picked from commit e134a1aa36027fb3c8bd9493028072365b19479b)

Co-authored-by: Serhiy Storchaka <storchaka@gmail.com>
Co-authored-by: Claude Opus 4.8 <noreply@anthropic.com>