Refactor to use RepositoriesProxy module

app/workers/thumbnail_generator_worker.rb

 class ThumbnailGeneratorWorker
 
   include Sidekiq::Worker
+  include RepositoriesProxy
 
   def perform(learning_object_id)
 
@@ -11,7 +12,7 @@ class ThumbnailGeneratorWorker
     default_size = "600x600"
     default_thumbnail = "#{thumbnails_dir}/default_thumbnail.jpg"
 
-    item = item_database_repository.find(learning_object_id)
+    item = learning_object_repository.find(learning_object_id)
     retrieve_link = item.get_bitstream_retrievelink_of "ORIGINAL"
     filename = item.get_bitstream_filename_of "ORIGINAL"
 
@@ -45,10 +46,6 @@ class ThumbnailGeneratorWorker
 
   private
 
-  def item_database_repository
-    @item_database_repository ||= Portalmec::Application.repository.for(:learning_object)
-  end
-
   def encode_hash_from(object)
     Digest::SHA1.hexdigest object
   end