About half of the usages were not using `force` anyways, and the other
half presumably just got confused about what "force" really means in
this context (which is "ignore nonexistent files").
The only 'legitimate' user, which is `rm`, instead now handles this
completely internally instead.
We have a new, improved string type coming up in AK (OOM aware, no null
state), and while it's going to use UTF-8, the name UTF8String is a
mouthful - so let's free up the String name by renaming the existing
class.
Making the old one have an annoying name will hopefully also help with
quick adoption :^)
