x86_64: remove __smp_alt* sections

Leftovers from the removal of the more general (but abandoned) SMP
alternatives.

Signed-off-by: Jan Beulich <jbeulich@novell.com>
Signed-off-by: Andi Kleen <ak@suse.de>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>