s390/time: remove select CLOCKSOURCE_VALIDATE_LAST_CYCLE again

Sven Schnelle reported that setting CLOCKSOURCE_VALIDATE_LAST_CYCLE
doesn't make sense: even if our tod clock overflows delta calculation
(now - last) with unsigned 64 bit values will still be correct.

Therefore revert commit 555701a ("s390/time: select
CLOCKSOURCE_VALIDATE_LAST_CYCLE").

Fixes: 555701a ("s390/time: select CLOCKSOURCE_VALIDATE_LAST_CYCLE")
Reported-by: Sven Schnelle <svens@linux.ibm.com>
Signed-off-by: Heiko Carstens <hca@linux.ibm.com>

arch/s390/Kconfig

@@ -126,7 +126,6 @@ config S390
 	select HAVE_ARCH_JUMP_LABEL_RELATIVE
 	select HAVE_ARCH_KASAN
 	select HAVE_ARCH_KASAN_VMALLOC
-	select CLOCKSOURCE_VALIDATE_LAST_CYCLE
 	select CPU_NO_EFFICIENT_FFS if !HAVE_MARCH_Z9_109_FEATURES
 	select HAVE_ARCH_SECCOMP_FILTER
 	select HAVE_ARCH_SOFT_DIRTY