[Driver] Remove a bunch of unnecessary REQUIRES constraints (#94055)

Removed foo-registered-target constraints from a bunch of tests, because
mostly the driver doesn't need to have a target availabile. I ran
check-clang-driver using a build with only the XCore target, and these
all passed.

There are ~50 tests that still have foo-registered-target, and it looks
like most of them are either doing codegen when they don't need to, or
don't really belong in the Driver tests. But that's a task for another
day.