Remove unused `with_custom_integration_compared_to`

The method is not called, and calls a class method on `Project` that
no longer exists.

app/controllers/concerns/integrations_actions.rb

@@ -34,10 +34,6 @@ module IntegrationsActions
     end
   end
 
-  def custom_integration_projects
-    Project.with_custom_integration_compared_to(integration).page(params[:page]).per(20)
-  end
-
   def test
     render json: {}, status: :ok
   end