Revert "Merge branch 'issues/15127' into 'master'"

This reverts merge request !3647

app/models/user.rb

@@ -789,6 +789,11 @@ class User < ActiveRecord::Base
                             other.select(:id)])
   end
 
+  # Added according to https://github.com/plataformatec/devise/blob/7df57d5081f9884849ca15e4fde179ef164a575f/README.md#activejob-integration
+  def send_devise_notification(notification, *args)
+    devise_mailer.send(notification, self, *args).deliver_later
+  end
+
   def ensure_external_user_rights
     return unless self.external?
 

config/initializers/devise_async.rb

 Devise::Async.backend = :sidekiq
-Devise::Async.queue = :mailers