Back out "Fix error in simple_spawner.gd with Godot 4.2.2"

This backs out commit 99e2dc1.

We now require Godot 4.3.

Author: wjt

addons/block_code/simple_spawner/simple_spawner.gd

@@ -89,7 +89,7 @@ func spawn_once():
 	if scenes.size() == 0:
 		return
 
-	_spawned_scenes = _spawned_scenes.filter(func(instance): return is_instance_valid(instance))
+	_spawned_scenes = _spawned_scenes.filter(is_instance_valid)
 
 	if spawn_limit != 0 and _spawned_scenes.size() >= spawn_limit:
 		if limit_behavior == LimitBehavior.NO_SPAWN: