CLN: Enforce deprecations for EA.fillna
- [ ] closes #xxxx (Replace xxxx with the GitHub issue number)
- [ ] [Tests added and passed](https://pandas.pydata.org/pandas-docs/dev/development/contributing_codebase.html#writing-tests) if fixing a bug or adding a new feature
- [ ] All [code checks passed](https://pandas.pydata.org/pandas-docs/dev/development/contributing_codebase.html#pre-commit).
- [ ] Added [type annotations](https://pandas.pydata.org/pandas-docs/dev/development/contributing_codebase.html#type-hints) to new arguments/methods/functions.
- [ ] Added an entry in the latest `doc/source/whatsnew/vX.X.X.rst` file if fixing a bug or adding a new feature.

Ref: #53621

Ran into a little trouble here - `NDFrame.fillna` has a `limit` argument that wasn't deprecated and works, but `EA.fillna` has this deprecated and is currently ignored. Currently this PR keeps the `limit` argument in `EA.fillna` and removes the deprecation, but the implementation still ignores it. If we want to keep it, I plan on doing a followup implementing `limit` across all EAs (I think this should be straightforward except for maybe Sparse - not sure). 

As an alternative, we could also deprecate `limit` on `NDFrame.fillna` (not my preference), and then I can keep but not enforce the deprecation on `EA.fillna` here.

cc @jbrockmendel 
keeping the limit argument sounds good to me, feel free to merge when ready Thanks @rhshadrach