Remove unused variables

- google_auth_version
- znc_version

vars/defaults.yml

 collectd_librato_email: "" # (optional)
 collectd_librato_api_token: "" # (optional)
 
-# google authenticator
-google_auth_version: 1.0
-
 # database
 db_admin_username: 'postgres'
 # db_admin_password: (required)
 
 # ircbouncer
-znc_version: 1.4
 # irc_nick: (required)
 # irc_ident: (required)
 # irc_realname: (required)