[entity] Stop linking to external site for external entities This behaviour was ok when we had "true" multi-sources but its rather painful with datafeed sources. Also, it makes absolute_url() costlier than what it should. Besides, it relies on cw_metainformation()['source'] that is pending for removal. Instead, add a link to the original object in the metadata view (the one that displays eid and source at the bottom right corner of the primary view). Related to #15538288.

[datafeed] Drop entity deletion handling in the default source / parser This should be handled by specific parser to avoid using "entities.asource". Reimplement it in the ldap parser. Related to #15538288

[sources] Drop 'moved_entities' table handling This was clumsy and could be handled using exturi / cwsource, as the ldap source now does.