## Description:
More fixes flagged by pylint 2 that don't hurt to have before the actual pylint 2 upgrade (which I'll submit soon).
## Checklist:
- [ ] The code change is tested and works locally.
- [x] Local tests pass with `tox`. **Your PR cannot be merged unless tests pass**
* No longer require pyunify during tests
* No longer require cast during tests
* No longer required dependency for tests
* No longer require pymochad for tests
* Astral is a core dependency
* Avoid having to install datadog dependency during tests
* CMUS test doesn't test anything
* Frontier Silicon doesn't test anything
* No longer require mutagen
* Update requirements_test_all.txt
* Remove stale comment
