CLN: Consistent pandas.util.testing imports in remaining test suite
Part of #29272 

Fyi: All changes are generated from a script posted in the issue.

- [x] tests added / passed
- [x] passes `black pandas`
- [x] passes `git diff upstream/master -u -- "*.py" | flake8 --diff`

Fyi: When the remaining PRs of this are merged, I'll add another one to add the linting rule - then we can close the issue
thanks @SaturnFromTitan 

when the last of the imports are done, can you prepare a change to fail the CI on incorrect imports. this go in the ci/code_checks.sh script, see how we exclude numpy.testing (but maybe need to be a bit more sophistacted here).