unneeded code in relationship_notification_hook

[bencc]

There is no need to check for ElggRelationship, 'create' and 'friend' in the following function because the event handler already takes care of that.
​https://github.com/Elgg/Elgg/blob/master/engine/lib/relationships.php#L611

function relationship_notification_hook($event, $object_type, $object) {
	global $CONFIG;

	if (
		($object instanceof ElggRelationship) &&
		($event == 'create') &&
		($object_type == 'friend')
	) {
		$user_one = get_entity($object->guid_one);
		$user_two = get_entity($object->guid_two);

		// Notify target user
		return notify_user($object->guid_two, $object->guid_one,
			elgg_echo('friend:newfriend:subject', array($user_one->name)),
			elgg_echo("friend:newfriend:body", array($user_one->name, $user_one->getURL()))
		);
	}
}

/** Register event to listen to some events **/
elgg_register_event_handler('create', 'friend', 'relationship_notification_hook');

[Cash Costello]

Fixes #3585 do not need to check parameters because was registered for only one event

Changeset: f3240e1da73d4a89e379c0c34f8ce86f460e18dc