[compat] Remove PY2 compat artefacts

- No need to specific types
- Remove __future__ imports

polymorphic/tests/test_multidb.py

@@ -1,5 +1,3 @@
-from __future__ import print_function
-
 from django.contrib.contenttypes.models import ContentType
 from django.db.models import Q
 from django.test import TestCase