Warn for unnecessary :func: parentheses

Sometimes authors add parentheses like this:

```rst
: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: 

```rst
:func:`!locale.resetlocale`
```

Re: https://github.com/python/cpython/pull/123132/files#r1721239362