Internal helper to delete a low level key, and then if the top-level is empty, get that one too.
function _full_delete(hash, key1, key2){
	    if( key1 && key2 && hash &&
		hash[key1] && hash[key1][key2] ){
		    delete hash[key1][key2];
		}
	    if( us.isEmpty(hash[key1]) ){
		delete hash[key1];
	    }
	}