[repository] Drop the entities.extid column and associated cache
This was not necessary anymore with promoted usage of the new data import API.
Turn repository's _type_extid_cache to _type_cache with only the entity's type
as key.
This introduces an backward incompatible change: entity_metas dict doesn't
contains anymore the extid key, but it doesn't seem used at all anywhere, so
this sounds acceptable.
Closes #15538317
.. _core_module:
:mod:`cubicweb.pyramid.core`
----------------------------
.. automodule:: cubicweb.pyramid.core
.. autofunction:: includeme
.. autofunction:: cw_to_pyramid
.. autofunction:: render_view
.. autofunction:: repo_connect
.. autofunction:: get_principals
.. autoclass:: CubicWebPyramidRequest
:show-inheritance:
:members:
.. autofunction:: _cw_session
.. autofunction:: _cw_cnx
.. autofunction:: _cw_request