s390: remove couple of duplicate includes

Removing couple of duplicate includes, found by "make includecheck".
That leaves 1 duplicate include in arch/s390/kernel/entry.S, which is
there for a reason (it includes generated asm/syscall_table.h twice).

Signed-off-by: Vasily Gorbik <gor@linux.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>