Duplicate debug handling in Factory::getDbo()

An odd error reported at http://joomlacode.org/gf/project/joomla/tracker/?action=TrackerItemEdit&tracker_item_id=31108 led to it being pointed out that setDebug() is being run in both `getDbo()` and `createDbo()`.  This PR matches the proposed patch to the CMS and drops the handling in `getDbo()`.

I know we want to get rid of this code, but while it's in the repo, it might as well be efficient code ;-)