Remove duplicate information

Author: fabpot

mailer.rst

@@ -221,7 +221,6 @@ OhMySMTP             ohmysmtp+smtp://API_TOKEN@default                    n/a
     revokes your App Passwords when you change your Google Account password and then
     you need to generate a new one.
     Using other methods (like ``XOAUTH2`` or the ``Gmail API``) are not supported currently.
-    You should use Gmail for testing purposes only and use a real provider in production. 
 
 .. tip::