oidc: Remove groups attribute

It leads to crash with Django.

This reverts a tiny portion of #669.

Fixes #690

social_core/backends/open_id_connect.py

@@ -248,5 +248,4 @@ def get_user_details(self, response):
             'fullname': response.get('name'),
             'first_name': response.get('given_name'),
             'last_name': response.get('family_name'),
-            'groups': response.get('groups'),    # not standardized but widely implemented
         }