Fix up warnings

- the default auto-increment primary key field type is now
  configurable, and Django's check command issues a warning if you are
  just assuming the historical behavior of using AutoField.

- Django 3.2 brings in automatic AppConfig discovery, so all of our
  explicit `default_app_config = ...` assignments in __init__.py
  modules are no longer needed, and raise a RemovedInDjango41Warning.

awx/conf/__init__.py

@@ -7,8 +7,6 @@ from django.utils.module_loading import autodiscover_modules
 # AWX
 from .registry import settings_registry
 
-default_app_config = 'awx.conf.apps.ConfConfig'
-
 
 def register(setting, **kwargs):
     settings_registry.register(setting, **kwargs)

awx/main/__init__.py

@@ -1,4 +1,2 @@
 # Copyright (c) 2015 Ansible, Inc.
 # All Rights Reserved.
-
-default_app_config = 'awx.main.apps.MainConfig'

awx/settings/defaults.py

@@ -41,6 +41,11 @@ else:
 DEBUG = True
 SQL_DEBUG = DEBUG
 
+# FIXME: it would be nice to cycle back around and allow this to be
+# BigAutoField going forward, but we'd have to be explicit about our
+# existing models.
+DEFAULT_AUTO_FIELD = 'django.db.models.AutoField'
+
 DATABASES = {
     'default': {
         'ENGINE': 'django.db.backends.sqlite3',

awx/sso/__init__.py

@@ -1,4 +1,2 @@
 # Copyright (c) 2015 Ansible, Inc.
 # All Rights Reserved.
-
-default_app_config = 'awx.sso.apps.SSOConfig'

awx/ui/__init__.py

@@ -1,4 +1,2 @@
 # Copyright (c) 2015 Ansible, Inc.
 # All Rights Reserved.
-
-default_app_config = 'awx.ui.apps.UIConfig'