Fix 'Models aren't loaded yet' warning on import

categories.registration._process_registry was being called in
categories/__init__.py, but since Django 1.9 it hasn't been possible to
perform operations with models until the app registry is fully
loaded. Currently the `AppRegistryNotReady` exception is being caught
and printed, which means it is never actually executed on load.

Since this code isn't currently doing anything (other than emitting a
print() of a warning), I've removed it.

categories/__init__.py

@@ -21,16 +21,3 @@ __version__ = get_version()
 
 
 default_app_config = 'categories.apps.CategoriesConfig'
-
-
-def register():
-    from categories import settings
-    from categories.registration import (_process_registry, registry)
-    _process_registry(settings.FK_REGISTRY, registry.register_fk)
-    _process_registry(settings.M2M_REGISTRY, registry.register_m2m)
-
-
-try:
-    register()
-except Exception as e:
-    print(e)

categories/tests/test_mgmt_commands.py

@@ -3,11 +3,22 @@ from unittest import skip
 
 from django.core import management
 from django.core.management.base import CommandError
+from django.db import connection
 from django.test import TestCase
 
 
 class TestMgmtCommands(TestCase):
 
+    @classmethod
+    def setUpClass(cls):
+        connection.disable_constraint_checking()
+        super(TestMgmtCommands, cls).setUpClass()
+
+    @classmethod
+    def tearDownClass(cls):
+        super(TestMgmtCommands, cls).tearDownClass()
+        connection.enable_constraint_checking()
+
     def test_add_category_fields(self):
         management.call_command('add_category_fields', verbosity=0)