TST: Eliminating references to pandas.util.testing.choice
- [x] closes #12386
- [x] tests passed
- [x] passes `git diff upstream/master | flake8 --diff`

Want to remove pandas.util.testing.choice.  First eliminating all
references to it.  Doing this in more than one commit as there are a lot
of them.
#12386

gr8!

can you add a whatsnew (even though this is a testing function, technically was in 'public' space, you can put in bug fixes).
squash as well. ping when green.
 I'm having trouble squashing.  When I do the following:

`git rebase -i HEAD~5`

I see a bunch of other people's commits also, not just mine.  Perhaps this is because I didn't branch off my fork, but worked on it directly?
 Yeah, it's typically best to work off feature branches.

What happens if you `git rebase -i upstream/master` and put all your commits at the end by moving those lines down, and the squash? Otherwise we can just make a new pull request from another branch (`git co -b remove-tm-choice`)
 I'll make a new pull request from another branch tomorrow evening (and close this one afterwards).  Thanks for the suggestion.
 Or I guess I'll close this one first to eliminate confusion.  Anyway, I'll work on it tomorrow night.
 you don't need a new PR. just rebase and force push.
 ```
git checkout master
git pull
git checkout <thisbranch>
git pull --rebase master
```

fix anything, then force push (`-f`)
