s390: remove test_facility(2) (== z/Architecture mode active) checks

Given that the kernel now always runs in 64 bit mode, it is
pointless to check if the z/Architecture mode is active.
Remove the checks.

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