[massive store] Drop deprecated code
This is not a desired part of the store API. Mapping between extid and eid
should be done by the importer.
This had been backported from the dataio cube, but not one seems to rely on it
yet, so don't provide any backward compat.
3.34 (UNRELEASED)
=================
New features
------------
* Various bits of a CubicWeb application configuration can be now be
overridden through environments variables matching configuration option
names prefixed by ``CW_`` (for instance ``CW_BASE_URL``).
* Cubes are now standard Python packages named as ``cubicweb_<cubename>``.
They are not anymore installed in ``<prefix>/share/cubicweb/cubes``. Their
discovery by CubicWeb is handled by a new setuptools entry point
``cubicweb.cubes``. A backward compatibility layer is kept for "legacy"
cubes.