Removed module-level functions for the app cache.

Since the original ones in django.db.models.loading were kept only for
backwards compatibility, there's no need to recreate them. However, many
internals of Django still relied on them.

They were also imported in django.db.models. They never appear in the
documentation, except a quick mention of get_models and get_app in the
1.2 release notes to document an edge case in GIS. I don't think that
makes them a public API.

This commit doesn't change the overall amount of global state but
clarifies that it's tied to the app_cache object instead of hiding it
behind half a dozen functions.

django/core/management/base.py

@@ -342,11 +342,11 @@ class AppCommand(BaseCommand):
     args = '<appname appname ...>'
 
     def handle(self, *app_labels, **options):
-        from django.db import models
+        from django.apps import app_cache
         if not app_labels:
             raise CommandError('Enter at least one appname.')
         try:
-            app_list = [models.get_app(app_label) for app_label in app_labels]
+            app_list = [app_cache.get_app(app_label) for app_label in app_labels]
         except (ImproperlyConfigured, ImportError) as e:
             raise CommandError("%s. Are you sure your INSTALLED_APPS setting is correct?" % e)
         output = []