[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
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