Cleanup: Get rid of dynamic property enumerator callbacks in QV4::Object

These are not needed anymore with the most recent portings away from v8.
Implemented Object::__hasProperty__ by means of query/queryIndexed.

Change-Id: Id02057a34c44a8c4e71912a5b5379740f09ef05d
Reviewed-by: Lars Knoll <lars.knoll@digia.com>