add: if (use_db) db_remove_presence_tuple(_p, _t);
context: void remove_presence_tuple(presentity_t *_p, presence_tuple_t *_t){	presence_tuple_t *tuples = _p->tuples;	if (tuples == _t) {		_p->tuples = _t->next;	}	if (_t->prev) {		_t->prev->next = _t->next;	}	if (_t->next) {		_t->next->prev = _t->prev;	}}