CI: Moving CircleCI build to Travis
- [X] xref #23821
- [ ] tests added / passed
- [ ] passes `git diff upstream/master -u -- "*.py" | flake8 --diff`
- [ ] whatsnew entry

Moving the CircleCI job to Travis. In a separate PR, I'll some jobs not using mysql and postgres to Azure, to balance things, and make the whole CI finish earlier.