[devtools] remove the remaining bw compat for old-style tests
It is just:
* dangerously untested right now
* on the path of further bw compat removal (cnxset handling)
webtest drops an apparently pointless .login call
Related to #3933480.
usr/lib/PY_VERSION/*-packages/cubicweb/server/
usr/lib/PY_VERSION/*-packages/cubicweb/hooks/
usr/lib/PY_VERSION/*-packages/cubicweb/sobjects/
usr/lib/PY_VERSION/*-packages/cubicweb/schemas/
usr/share/cubicweb/migration/