Remove unused mailers.

app/mailers/user_mailer.rb

@@ -8,14 +8,6 @@ class UserMailer < ActionMailer::Base
     mail(:to => "#{dmail.to.name} <#{dmail.to.email}>", :subject => "#{Danbooru.config.app_name} - Message received from #{dmail.from.name}")
   end
 
-  def upgrade(user, email)
-    mail(:to => "#{user.name} <#{email}>", :subject => "#{Danbooru.config.app_name} account upgrade")
-  end
-
-  def upgrade_fail(email)
-    mail(:to => "#{user.name} <#{email}>", :subject => "#{Danbooru.config.app_name} account upgrade")
-  end
-
   def forum_notice(user, forum_topic, forum_posts)
     @user = user
     @forum_topic = forum_topic