remove useless upload topic direct association

db/migrate/20130615073305_remove_topic_id_from_uploads.rb

@@ -0,0 +1,9 @@
+class RemoveTopicIdFromUploads < ActiveRecord::Migration
+  def up
+    remove_column :uploads, :topic_id
+  end
+
+  def down
+    add_column :uploads, :topic_id, :interger, null: false, default: -1
+  end
+end