Nix setting from the docs

We don't have it set up like this on our machines and if you don't have
redis running, then this causes a bunch of odd problems.

Better to nix it from the docs.

docs/hacking_howto.rst

@@ -148,7 +148,6 @@ Start by creating a file named ``settings_local.py`` in the
             }
         }
 
-    CACHE_MACHINE_USE_REDIS = True
     CACHE_MIDDLEWARE_ALIAS = 'default'
     CACHE_MIDDLEWARE_KEY_PREFIX = ''
     CACHE_MIDDLEWARE_SECONDS = 600

docs/installation.rst

@@ -132,7 +132,6 @@ For local development you will want to add the following settings::
         }
 
     CACHE_BACKEND = 'caching.backends.memcached://localhost:11211'
-    CACHE_MACHINE_USE_REDIS = True
     CACHE_MIDDLEWARE_ALIAS = 'default'
     CACHE_MIDDLEWARE_KEY_PREFIX = ''
     CACHE_MIDDLEWARE_SECONDS = 600