MIPS: IRQ: remove orphan declarations from arch/mips/include/asm/irq.h

All uses of free_irqno() and alloc_legacy_irqno() were removed
by commit 69a07a41 ("MIPS: SGI-IP27: rework HUB interrupts"),
so remove the orphan declarations, too.
Signed-off-by: Gaosheng Cui <cuigaosheng1@huawei.com>
Signed-off-by: Thomas Bogendoerfer <tsbogend@alpha.franken.de>

arch/mips/include/asm/irq.h

@@ -64,8 +64,6 @@ extern void arch_init_irq(void);
 extern void spurious_interrupt(void);
 
 extern int allocate_irqno(void);
-extern void alloc_legacy_irqno(void);
-extern void free_irqno(unsigned int irq);
 
 /*
  * Before R2 the timer and performance counter interrupts were both fixed to