Include AV::Layouts directly in AM::Base

No need to do this in railtie as AM depends on AV either way

actionmailer/lib/action_mailer/base.rb

@@ -373,6 +373,8 @@ module ActionMailer
     include AbstractController::AssetPaths
     include AbstractController::Callbacks
 
+    include ActionView::Layouts
+
     PROTECTED_IVARS = AbstractController::Rendering::DEFAULT_PROTECTED_INSTANCE_VARIABLES + [:@_action_has_layout]
 
     def _protected_ivars # :nodoc:

actionview/lib/action_view/railtie.rb

@@ -42,12 +42,6 @@ module ActionView
       end
     end
 
-    initializer "action_view.setup_action_mailer", before: :add_view_paths do |app|
-      ActiveSupport.on_load(:action_mailer) do
-        ActionMailer::Base.send(:include, ActionView::Layouts)
-      end
-    end
-
     rake_tasks do
       load "action_view/tasks/dependencies.rake"
     end