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.