perf: pmuv3: Remove comments from armv8pmu_[enable|disable]_event()

The comments in armv8pmu_[enable|disable]_event() are blindingly obvious,
and does not contribute in making things any better. Let's drop them off.
Functional change is not intended.

Cc: Will Deacon <will@kernel.org>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: linux-arm-kernel@lists.infradead.org
Cc: linux-kernel@vger.kernel.org
Suggested-by: Mark Rutland <mark.rutland@arm.com>
Signed-off-by: Anshuman Khandual <anshuman.khandual@arm.com>