Auto-delete all auto-guides

The auto-guide gadget is great while building out a level using existing assets. But it can lead to there being hundreds or thousands of these gadgets hanging out in a scene when they'll never be used again. It would be super useful to be able to go to tools > "delete all auto-guides" or something like that once we're done with laying out the scene, or if we need more gameplay > things thermo for things that are used in gameplay.