[sobjects] Drop custom unique constraint checks in user registration service
This constraints (on unique CWUser's login and EmailAddress's login) are
handled by the backend.
This follows "[hooks/integrity] kill CheckUniqueHook".
Extend test for the ValidationError along the way.
from cubicweb.schemas.base import in_group, CWSourceSchemaConfig
# copy __permissions__ to avoid modifying a shared dictionary
in_group.__permissions__ = in_group.__permissions__.copy()
in_group.__permissions__['read'] = ('managers',)
cw_for_source = CWSourceSchemaConfig.get_relation('cw_for_source')
cw_for_source.__permissions__ = {'read': ('managers', 'users'),
'add': ('managers',),
'delete': ('managers',)}