s390/sclp: remove call home support

This feature has never been used, so remove it.

Acked-by: Vasily Gorbik <gor@linux.ibm.com>
Acked-by: Hendrik Brueckner <brueckner@linux.ibm.com>
Signed-off-by: Heiko Carstens <heiko.carstens@de.ibm.com>
Signed-off-by: Vasily Gorbik <gor@linux.ibm.com>