[ARM] 3199/1: Remove bogus function prototype from arch-pxa/irq.h

Patch from Deepak Saxena

This looks like a leftover from 2.4 days...
Signed-off-by: Deepak Saxena <dsaxena@plexity.net>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>

include/asm-arm/arch-pxa/irq.h

@@ -12,8 +12,3 @@
 
 #define fixup_irq(x)	(x)
 
-/*
- * This prototype is required for cascading of multiplexed interrupts.
- * Since it doesn't exist elsewhere, we'll put it here for now.
- */
-extern void do_IRQ(int irq, struct pt_regs *regs);