Fix for older Perls that use depth-first method resolution

The call to delete() on line 87 was getting resolved to UR::Object::delete (because of
the dfs resolution of ChildSingleton->SomeSingleton->Parent->UR::Object) instead of
going to UR::Singleton::delete()

Change-Id: Idd77b7ef345d5da71177e2e50962830385fcc867