Completely remove traces of caching.backends settings.

Most of this work landed already in
6a8fc341da and
91605a4c1f so this is just a follow-up to
remove all other traces.

The removed comment is no longer true, Django received all the necessary
fixes for LocMemCache. On the other hand, LoMemCache is no longer used
for a regular local setup because we are using memcached and try to be
as close to production as possible so this won't change anytime
soon.

docs/topics/install/deprecated/advanced-installation.rst

@@ -49,7 +49,7 @@ settings already use the following, so you shouldn't need to change anything::
 
     CACHES = {
         'default': {
-            'BACKEND': 'caching.backends.memcached.MemcachedCache',
+            'BACKEND': 'django.core.cache.backends.memcached.MemcachedCache',
             'LOCATION': ['localhost:11211'],
             'TIMEOUT': 500,
         }

settings.py

@@ -23,21 +23,11 @@ FILESYSTEM_CACHE_ROOT = os.path.join(TMP_PATH, 'cache')
 # Disable cache-machine locally and in tests to prepare for its removal.
 CACHE_MACHINE_ENABLED = False
 
-# Using locmem deadlocks in certain scenarios. This should all be fixed,
-# hopefully, in Django1.7. At that point, we may try again, and remove this to
-# not require memcache installation for newcomers.
-# A failing scenario is:
-# 1/ log in
-# 2/ click on "Submit a new addon"
-# 3/ click on "I accept this Agreement" => request never ends
-#
-# If this is changed back to locmem, make sure to use it from "caching" (by
-# default in Django for locmem, a timeout of "0" means "don't cache it", while
-# on other backends it means "cache forever"):
-#      'BACKEND': 'caching.backends.locmem.LocMemCache'
+# We are setting memcached here to make sure our local setup is as close
+# to our production system as possible.
 CACHES = {
     'default': {
-        'BACKEND': 'caching.backends.memcached.MemcachedCache',
+        'BACKEND': 'django.core.cache.backends.memcached.MemcachedCache',
         'LOCATION': os.environ.get('MEMCACHE_LOCATION', 'localhost:11211'),
     },
     'filesystem': {