s390/zcrypt: remove unused functions and declarations

The AP bus code is not available as kernel module any more.
There was some leftover code dealing with kernel module
exit which has been removed with this patch.

Signed-off-by: Harald Freudenberger <freude@linux.vnet.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>