BREAKING CHANGE: Removes all remaining Paver commands including `pavelib/prereqs.py:*` and `pavelib/assets.py:*`. BREAKING CHANGE: Removes `./manage.py [lms|cms] compile_sass`, which was just a wrapper around Paver commands. BREAKING CHANGE: Removes paver.txt. Operators should install testing.txt instead. Part of: https://github.com/openedx/edx-platform/issues/34467