s390: Get rid of oprofile leftovers

perf_pmu_name() and perf_num_counters() are unused. Drop them.

Signed-off-by: Marc Zyngier <maz@kernel.org>
Acked-by: Heiko Carstens <hca@linux.ibm.com>
Link: https://lore.kernel.org/r/20210414134409.1266357-4-maz@kernel.org