[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.
### Requirements for tests in various cubicweb/**/test directories. ###
## shared by several test folders
cubicweb-card
docutils
Twisted < 16.0.0
webtest
## cubicweb/test
Pygments
mock
#fyzz XXX pip install fails
cubicweb-file
cubicweb-localperms
cubicweb-tag
## cubicweb/devtools/test
flake8
## cubicweb/hooks/test
psycopg2
## cubicweb/pyramid/test
pyramid >= 1.5.0
waitress >= 0.8.9
wsgicors >= 0.3
pyramid_multiauth
## cubicweb/sobject/test
cubicweb-comment