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/models/mixins.py

@@ -24,7 +24,7 @@ from awx.main.utils import parse_yaml_or_json, get_custom_venv_choices, get_lice
 from awx.main.utils.execution_environments import get_default_execution_environment
 from awx.main.utils.encryption import decrypt_value, get_encryption_key, is_encrypted
 from awx.main.utils.polymorphic import build_polymorphic_ctypes_map
-from awx.main.fields import JSONField, AskForField
+from awx.main.fields import AskForField
 from awx.main.constants import ACTIVE_STATES
 
 
@@ -103,12 +103,7 @@ class SurveyJobTemplateMixin(models.Model):
     survey_enabled = models.BooleanField(
         default=False,
     )
-    survey_spec = prevent_search(
-        JSONField(
-            blank=True,
-            default=dict,
-        )
-    )
+    survey_spec = prevent_search(models.JSONField(default=dict, blank=True))
     ask_variables_on_launch = AskForField(blank=True, default=False, allows_field='extra_vars')
 
     def survey_password_variables(self):
@@ -370,10 +365,11 @@ class SurveyJobMixin(models.Model):
         abstract = True
 
     survey_passwords = prevent_search(
-        JSONField(
-            blank=True,
+        models.JSONField(
             default=dict,
             editable=False,
+            null=True,
+            blank=True,
         )
     )