Improved performance of notification preloading (#15640)

* Improved performance of notification preloading

* Remove Cacheable from Notification

* Fix test

spec/controllers/application_controller_spec.rb

@@ -349,10 +349,6 @@ describe ApplicationController, type: :controller do
       expect(C.new.cache_collection(raw, Object)).to eq raw
     end
 
-    context 'Notification' do
-      include_examples 'cacheable', :notification, Notification
-    end
-
     context 'Status' do
       include_examples 'cacheable', :status, Status
     end