function unlink_effect(effect) {
	var parent = effect.parent;
	var prev = effect.prev;
	var next = effect.next;

	if (prev !== null) prev.next = next;
	if (next !== null) next.prev = prev;

	if (parent !== null) {
		if (parent.first === effect) parent.first = next;
		if (parent.last === effect) parent.last = prev;
	}
}
Detach an effect from the effect tree, freeing up memory and
reducing the amount of work that happens on subsequent traversals
@param {Effect} effect