Fixed #18220 -- Removed the CACHE_BACKEND setting, as per official deprecation timeline.

Thanks Ramiro Morales for the review.

django/core/cache/__init__.py

@@ -64,42 +64,6 @@ def parse_backend_uri(backend_uri):
 
     return scheme, host, params
 
-if not settings.CACHES:
-    legacy_backend = getattr(settings, 'CACHE_BACKEND', None)
-    if legacy_backend:
-        import warnings
-        warnings.warn(
-            "settings.CACHE_* is deprecated; use settings.CACHES instead.",
-            DeprecationWarning
-        )
-    else:
-        # The default cache setting is put here so that we
-        # can differentiate between a user who has provided
-        # an explicit CACHE_BACKEND of locmem://, and the
-        # default value. When the deprecation cycle has completed,
-        # the default can be restored to global_settings.py
-        settings.CACHE_BACKEND = 'locmem://'
-
-    # Mapping for new-style cache backend api
-    backend_classes = {
-        'memcached': 'memcached.CacheClass',
-        'locmem': 'locmem.LocMemCache',
-        'file': 'filebased.FileBasedCache',
-        'db': 'db.DatabaseCache',
-        'dummy': 'dummy.DummyCache',
-    }
-    engine, host, params = parse_backend_uri(settings.CACHE_BACKEND)
-    if engine in backend_classes:
-        engine = 'django.core.cache.backends.%s' % backend_classes[engine]
-    else:
-        engine = '%s.CacheClass' % engine
-    defaults = {
-        'BACKEND': engine,
-        'LOCATION': host,
-    }
-    defaults.update(params)
-    settings.CACHES[DEFAULT_CACHE_ALIAS] = defaults
-
 if DEFAULT_CACHE_ALIAS not in settings.CACHES:
     raise ImproperlyConfigured("You must define a '%s' cache" % DEFAULT_CACHE_ALIAS)