hv: fix 'Procedure is not called or referenced in code analysed'

MISRA-C requires that each function defined and declared shall be called
or referenced in code analyzed.

In some cases, we would like to keep the non-called functions for code
completeness, such as
vcpu_inject_extint/vcpu_inject_nmi/vcpu_inject_gp/vcpu_inject_pf
/vcpu_inject_ud/vcpu_inject_ac/vcpu_inject_ss.

This pacth removes some functions that are independent and are not
called in our code base.

Tracked-On: #861
Signed-off-by: Shiqing Gao <shiqing.gao@intel.com>
Acked-by: Eddie Dong <eddie.dong@intel.com>

hypervisor/arch/x86/ioapic.c

@@ -260,11 +260,6 @@ void ioapic_set_rte(uint32_t irq, union ioapic_rte rte)
 		rte.full);
 }
 
-uint32_t irq_gsi_num(void)
-{
-	return nr_gsi;
-}
-
 bool irq_is_gsi(uint32_t irq)
 {
 	return irq < nr_gsi;