Remove obsolete resource method in controllers

This method was used by controllers using the `Translatable` concern. We
forgot to remove it in commit 71601bd3f.

app/controllers/admin/legislation/processes_controller.rb

@@ -77,8 +77,4 @@ class Admin::Legislation::ProcessesController < Admin::Legislation::BaseControll
         image_attributes: image_attributes
       ]
     end
-
-    def resource
-      @process || ::Legislation::Process.find(params[:id])
-    end
 end