x86/entry: Remove now unused do_IRQ() declaration

do_IRQ() has been replaced by common_interrupt() in

  fa5e5c40 ("x86/entry: Use idtentry for interrupts")

Remove its now unused declaration.
Signed-off-by: Hao Lee <haolee.swjtu@gmail.com>
Signed-off-by: Borislav Petkov <bp@suse.de>
Link: https://lkml.kernel.org/r/20210103030834.GA15432@haolee.github.io

arch/x86/include/asm/irq.h

@@ -40,8 +40,6 @@ extern void native_init_IRQ(void);
 
 extern void __handle_irq(struct irq_desc *desc, struct pt_regs *regs);
 
-extern __visible void do_IRQ(struct pt_regs *regs, unsigned long vector);
-
 extern void init_ISA_irqs(void);
 
 extern void __init init_IRQ(void);