ARM: 6276/1: mach-shmobile: remove duplicate NR_IRQS_LEGACY

NR_IRQS_LEGACY is now defined in asm/irq.h,
so drop it in mach/irqs.h.

Signed-off-by: Magnus Damm <damm@opensource.se>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>