don't muck with production.rb, no longer supported

docs/INSTALL-email.md

@@ -1,13 +1,8 @@
 # Discourse Mail Setup Guide
 
-After following INSTALL-ubuntu.md your mailer settings should still be set (in
-`config/environments/production.rb`, remember) to:
-
-```ruby
-  config.action_mailer.delivery_method = :sendmail
-  config.action_mailer.sendmail_settings = {arguments: '-i'}
-```
+After following INSTALL-ubuntu.md your mailer settings should still be set.
 
+Out-of-the-box Discourse is configured to deliver mail locally via sendmail.
 That's great. Leave that there as we're going to try to get the mail to postfix
 ASAP so postfix do it's job and process the mail for delivery.