[repository] Drop deprecated extid2eid API and friends This will break cwxmlparser based sources. They should be rewritten using a specific parser, based on xml representation or on rqlio. This is harsh but allows a so big cleanup of the code base. Furthermore, it's necessary for asource/extid handling in the entities table which is costly for most app that don't care at all about that... In this cset, delete: * all extid2eid methods * repo._extid_cache handling * [before/after]_entity_insertion source callback * the cwxmlparser and update related tests, notably unittest_datafeed where 'repull' testing has been removed, since it's now handled by the dataimport API and should not be retested there. Related to #15538288 Closes #15538383

usr/lib/python2*/*-packages/cubicweb/dataimport/
usr/lib/python2*/*-packages/cubicweb/server/
usr/lib/python2*/*-packages/cubicweb/hooks/
usr/lib/python2*/*-packages/cubicweb/sobjects/
usr/lib/python2*/*-packages/cubicweb/schemas/
usr/share/cubicweb/migration/