Replace ActionMailer::Base#respond_to? with respond_to_missing?

actionmailer/lib/action_mailer/base.rb

@@ -541,8 +541,8 @@ def deliver_mail(mail) #:nodoc:
         end
       end
 
-      def respond_to?(method, include_private = false) #:nodoc:
+      def respond_to_missing?(method, include_private = false) #:nodoc:
-        super || action_methods.include?(method.to_s)
+        action_methods.include?(method.to_s)
       end
 
     protected