[S390] Remove smp_cpu_not_running.

smp_cpu_not_running() and cpu_stopped() are doing the same.
Remove one and also get rid of the last hard_smp_processor_id() leftover.

Signed-off-by: Heiko Carstens <heiko.carstens@de.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>