Remove references to T-Series
- [×] closes #xxxx
- [✓] tests added / passed
- [△] passes `git diff upstream/master -u -- "*.py" | flake8 --diff`
- [👊] whatsnew entry

This pull request removes any references to T-Series from the source code. It is a breaking change for any old code that relies on the old module name, so it will probably require a new major version release, but that is a small price to pay.