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

Signed-off-by: Marc Zyngier <maz@kernel.org>
Reviewed-by: Geert Uytterhoeven <geert+renesas@glider.be>
Link: https://lore.kernel.org/r/20210414134409.1266357-5-maz@kernel.org