dmails: don't save copies of outgoing dmails sent by DanbooruBot.

There's not much sense in saving copies of everything DanbooruBot sends
in DanbooruBot's inbox. They probably won't be checked so it just bloats
the dmails table.

app/models/dmail.rb

@@ -61,7 +61,10 @@ class Dmail < ActiveRecord::Base
       end
 
       def create_automated(params)
-        create_split(from: Danbooru.config.system_user, **params)
+        dmail = Dmail.new(from: Danbooru.config.system_user, **params)
+        dmail.owner = dmail.to
+        dmail.save
+        dmail
       end
     end