s390/vmur: remove unused pm related functions

The Power-management related functions are unused since
'commit 39421627 ("s390: remove broken hibernate / power management
support")'. Remove them from the unit-record device driver.

Signed-off-by: Vineeth Vijayan <vneethv@linux.ibm.com>
Signed-off-by: Heiko Carstens <hca@linux.ibm.com>