x86: remove reminder of i386 irqstat per cpu conversion

The i386 irqstat per cpu conversion left an bogus export of the old
irqstat array in the header file. Remove it.

[ tglx: arch/x86 adaptation ]

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Ingo Molnar <mingo@elte.hu>