Warn for unnecessary :func: parentheses

[hugovk]

Sometimes authors add parentheses like this:

:func:`!locale.resetlocale()`

But they're not needed, because Sphinx will add them anyway to the rendered output.

Sphinx Lint could warn so authors instead use:

:func:`!locale.resetlocale`

Re: https://github.com/python/cpython/pull/123132/files#r1721239362