x86: remove leftover unwind annotations

Impact: cleanup

These got left in needlessly when ret_from_fork got simplified.

Signed-off-by: Jan Beulich <jbeulich@novell.com>
LKML-Reference: <49B8F355.76E4.0078.0@novell.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>