cpumask: remove references to struct irqaction's mask field.

Impact: cleanup

It's unused, since about 1995.  So remove all initialization of it in
preparation for actually removing the field.

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
Acked-by: Thomas Gleixner <tglx@linutronix.de>

arch/powerpc/platforms/chrp/setup.c

@@ -472,7 +472,6 @@ static void __init chrp_find_openpic(void)
 #if defined(CONFIG_VT) && defined(CONFIG_INPUT_ADBHID) && defined(CONFIG_XMON)
 static struct irqaction xmon_irqaction = {
 	.handler = xmon_irq,
-	.mask = CPU_MASK_NONE,
 	.name = "XMON break",
 };
 #endif