s390: remove orphaned extern variables declarations
arch/s390/kernel/entry.h: suspend_zero_pages - only declaration left
after commit
394216275c7d ("s390: remove broken hibernate / power
management support")
arch/s390/include/asm/setup.h: vmhalt_cmd - only declaration left after
commit
99ca4e582d4a ("[S390] kernel: Shutdown Actions Interface")
arch/s390/include/asm/setup.h: vmpoff_cmd - only declaration left after
commit
99ca4e582d4a ("[S390] kernel: Shutdown Actions Interface")
Signed-off-by: Vasily Gorbik <gor@linux.ibm.com>