Removed confusing ALLOW_REGISTER setting.

ALLOW_REGISTER was no longer being used in determining whether you could
register for the app, so I've removed it to avoid additional local-dev /
production issues.

This closes #1613.

(imported from commit c928c6d350602d35f745ae1e60d734e4567885fc)

zproject/settings.py

@@ -586,10 +586,8 @@ TUTORIAL_ENABLED = True
 
 HOME_NOT_LOGGED_IN = '/login'
 if DEPLOYED:
-    ALLOW_REGISTER = False
     FULL_NAVBAR    = False
 else:
-    ALLOW_REGISTER = True
     FULL_NAVBAR    = True
 
 # For testing, you may want to have emails be printed to the console.