[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.

[flake8] cubicweb/dataimport/test/test_massive_store.py is now flake8 friendly

[massive store] Drop buggy log call PGHelper has no logger, the store has.