Unhide plt, beginners don't know how to import it.
Alter https://github.com/pandas-dev/pandas/pull/30274.

- [ ] closes #xxxx
- [ ] tests added / passed
- [ ] passes `black pandas`
- [ ] passes `git diff upstream/master -u -- "*.py" | flake8 --diff`
- [ ] whatsnew entry

pls don’t make multiple PRs for the same issue
instead just update the original 