Disable moveBefore experiment (#33348)

There seems to be some bugs still to work out in Chrome. See #33187. Additionally, since you can't really rely on this function existing across browsers, it's hard to depend on its behavior anyway. In fact, you now have a source of inconsistent behaviors across browsers to deal with. Ideally it would also be more widely spread in fake DOM implementations like JSDOM so that we can use it unconditionally. #33177. We still want to enable this since it's a great feature but maybe not until it's more widely available cross-browsers with fewer bugs.