[sources] Drop source support_entity / support_relation source API
this was used in the pre-datafeed area, it's not worth it anymore.
Its only valid usage was in authentication to detect if the source was
supporting CWUser, hence we now call it systematically and catch
NotImplementedError.
psycopg2
ldap3
cubicweb-basket
cubicweb-card
cubicweb-comment
cubicweb-file
cubicweb-localperms
cubicweb-tag