removing memchache mentions in comments

remove memcached folder as it is no longer needed, also address a couple grammatical errors

awx/settings/development.py

@@ -21,7 +21,6 @@ from split_settings.tools import optional, include
 # Load default settings.
 from .defaults import *  # NOQA
 
-# don't use memcache when running tests
 if "pytest" in sys.modules:
     CACHES = {
         'default': {