Replace all usage of customized json fields with the Django builtin

The event_data field on event models, however, is getting an
overridden version that retains the underlying text data type for the
column, to avoid a heavy data migration on those tables.

Also, certain of the larger tables are getting these fields with the
NOT NULL constraint turned off, to avoid a long migration.

Remove the django.utils.six monkey patch we did at the beginning of
the upgrade.

awx/main/tests/functional/conftest.py

@@ -15,7 +15,6 @@ from django.core.serializers.json import DjangoJSONEncoder
 from django.db.backends.sqlite3.base import SQLiteCursorWrapper
 
 # AWX
-from awx.main.fields import JSONBField
 from awx.main.models.projects import Project
 from awx.main.models.ha import Instance
 
@@ -755,11 +754,6 @@ def get_db_prep_save(self, value, connection, **kwargs):
     return value
 
 
-@pytest.fixture
-def monkeypatch_jsonbfield_get_db_prep_save(mocker):
-    JSONBField.get_db_prep_save = get_db_prep_save
-
-
 @pytest.fixture
 def oauth_application(admin):
     return Application.objects.create(name='test app', user=admin, client_type='confidential', authorization_grant_type='password')