x86, irq: Remove arch_probe_nr_irqs

So keep nr_irqs == NR_IRQS.  With radix trees is matters less.

Signed-off-by: Yinghai Lu <yinghai@kernel.org>
LKML-Reference: <1265793639-15071-33-git-send-email-yinghai@kernel.org>
Signed-off-by: H. Peter Anvin <hpa@zytor.com>