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/conf/migrations/0001_initial.py

@@ -2,7 +2,6 @@
 from __future__ import unicode_literals
 
 from django.db import migrations, models
-import jsonfield.fields
 from django.conf import settings
 
 
@@ -18,7 +17,7 @@ class Migration(migrations.Migration):
                 ('created', models.DateTimeField(default=None, editable=False)),
                 ('modified', models.DateTimeField(default=None, editable=False)),
                 ('key', models.CharField(max_length=255)),
-                ('value', jsonfield.fields.JSONField(null=True)),
+                ('value', models.JSONField(null=True)),
                 (
                     'user',
                     models.ForeignKey(related_name='settings', default=None, editable=False, to=settings.AUTH_USER_MODEL, on_delete=models.CASCADE, null=True),

awx/conf/migrations/0003_v310_JSONField_changes.py

@@ -1,12 +1,11 @@
 # -*- coding: utf-8 -*-
 from __future__ import unicode_literals
 
-from django.db import migrations
-import awx.main.fields
+from django.db import migrations, models
 
 
 class Migration(migrations.Migration):
 
     dependencies = [('conf', '0002_v310_copy_tower_settings')]
 
-    operations = [migrations.AlterField(model_name='setting', name='value', field=awx.main.fields.JSONField(null=True))]
+    operations = [migrations.AlterField(model_name='setting', name='value', field=models.JSONField(null=True))]