[ldap] Stop using entities table in ldap source authentication and parser
We may used cwuri for the same purpose, and do one more step towards deletion of
entities.extid column.
Related to #15538288
usr/lib/python2*/*-packages/cubicweb/entities/
usr/lib/python2*/*-packages/cubicweb/ext/
usr/share/cubicweb/cubes/
usr/lib/python2*/*-packages/cubicweb/*.py