CAllForumTopic::Delete

static function Delete($ID)
{
	$arTopic = [];
	if ($topic = BitrixForumTopic::getById($ID))
	{
		$arTopic = $topic->getData();
		$topic->remove();
	}
	unset($GLOBALS["FORUM_CACHE"]["TOPIC"][$ID]);
	unset($GLOBALS["FORUM_CACHE"]["TOPIC_FILTER"][$ID]);

/***************** Event onAfterTopicDelete ************************/
	foreach(GetModuleEvents("forum", "onAfterTopicDelete", true) as $arEvent)
		ExecuteModuleEventEx($arEvent, array(&$ID, $arTopic));
/***************** /Event ******************************************/
	return true;
}