remove most 3.10 bw compat
Related to #3799117.
The boxes and entityvcomponent objects cannot really be removed as they
are still used throughout the code base (and possible cubes).
This may be caused by a non-working deprecation and needs some more
work.
usr/lib/PY_VERSION/*-packages/cubicweb/entities/
usr/lib/PY_VERSION/*-packages/cubicweb/ext/
usr/share/cubicweb/cubes/
usr/lib/PY_VERSION/*-packages/cubicweb/*.py