TST (string dtype): clean-up assorted xfails
@jorisvandenbossche @WillAyd opening as draft and will add more to this PR over time (as I find solvable ones).
This pull request is stale because it has been open for thirty days with no activity. Please [update](https://pandas.pydata.org/pandas-docs/stable/development/contributing.html#updating-your-pull-request) and respond to this comment if you're still interested in working on this. Appears this PR has gone stale. Feel free to reopen if/when you have time to revisit