Remove MITX from the name of the features dict.

This is to correspond to the same fix in the edx platform.
https://github.com/edx/edx-platform/pull/1827

playbooks/roles/edxapp/defaults/main.yml

@@ -59,7 +59,7 @@ EDXAPP_CELERY_PASSWORD: 'celery'
 
 EDXAPP_PLATFORM_NAME: 'edX'
 
-EDXAPP_MITX_FEATURES:
+EDXAPP_FEATURES:
   AUTH_USE_OPENID_PROVIDER: true
   CERTIFICATES_ENABLED: true
   ENABLE_DISCUSSION_SERVICE: true
@@ -279,7 +279,7 @@ generic_env_config:  &edxapp_generic_env
   LOCAL_LOGLEVEL: $EDXAPP_LOG_LEVEL
   # default email backed set to local SMTP
   EMAIL_BACKEND: $EDXAPP_EMAIL_BACKEND
-  MITX_FEATURES: $EDXAPP_MITX_FEATURES
+  FEATURES: $EDXAPP_FEATURES
   WIKI_ENABLED: true
   SYSLOG_SERVER:  $EDXAPP_SYSLOG_SERVER
   SITE_NAME:  $EDXAPP_SITE_NAME