This reverts commit e0cc36f615f70061e034f5ba3f4e75330f51d3ca.
The problem is the following:
* With non-gis backends, gis_tests sub apps are not discovered
(see runtests.py)
* Consequently, the app_label is inferred from the gis_tests
AppConfig
* Then models with same names in different sub apps conflict
because of same model_name/app_label pair.