Deprecate skipna=None for mad
- [x] tests added / passed
- [x] Ensure all linting tests pass, see [here](https://pandas.pydata.org/pandas-docs/dev/development/contributing_codebase.html#pre-commit) for how to run them
- [x] whatsnew entry

hmm are any of the doc-string failures related here? (don't think so but hard to tell at a glance).

also in future, feel free to link to the deprecation removal issue when appropriate Could not find anything which is related. Will link to the issue in the future oh sorry what meant was add an entry in the deprecation removal issue (we have 1 master one)

i did for this one already - but FYI Sorry my answer was very misleading. I meant:

I could not find any failing doctests which are related to this pr.
Will link to the deprecation issue in the future.


Sorry for the confusion can you rebase and ping on green ping @jreback thanks @phofl 