fix object de-authorize failed.

app/models/prototype_auth.rb

@@ -51,8 +51,9 @@ class PrototypeAuth
   end
   
   def remove_operation(item,obj)
-    if (self.send item).include? obj
-       (self.send item).delete obj
+    item = (item.to_s.singularize == item.to_s) ? "#{item.to_s}_id" : "#{item.to_s.singularize}_ids"
+    if (self.send item).include? obj.id
+       (self.send item).delete obj.id
       self.save!
     else
       false #should put error message for user not existed in list