xen/x86: Remove is_periodic_irq() prototype

is_periodic_irq() was removed in the Fixes commit, but the prototype
remained.  Drop it now.

Fixes: ddc35d1cc9 ("[HVM] Enable more than one platform timer...")
Signed-off-by: Jason Andryuk <jason.andryuk@amd.com>
Acked-by: Andrew Cooper <andrew.cooper3@citrix.com>

xen/arch/x86/include/asm/hvm/vpic.h

@@ -35,6 +35,5 @@ void vpic_irq_negative_edge(struct domain *d, int irq);
 void vpic_init(struct domain *d);
 void vpic_reset(struct domain *d);
 int vpic_ack_pending_irq(struct vcpu *v);
-int is_periodic_irq(struct vcpu *v, int irq, int type);
 
 #endif  /* __ASM_X86_HVM_VPIC_H__ */