Revert optimization on query
Revert optimization on query

The optimization broke Postgres, due to a Django bug.

See:

* https://github.com/django-guardian/django-guardian/issues/366
* https://code.djangoproject.com/ticket/16055

This partially reverts commit 3cdfd12a8906cc91a386d12bcfdd0f12f527dfb9.

Closes: #366

lukaszb/django-guardian,lukaszb/django-guardian,benkonrath/django-guardian,rmgorman/django-guardian,rmgorman/django-guardian,lukaszb/django-guardian,benkonrath/django-guardian,benkonrath/django-guardian,rmgorman/django-guardian