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