s390/cmma: remove "cmma disable" code in case of dump again

This is not necessary anymore, since the offending code is gone with
the conversion to the memblock code.

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