kvm: Delete prototype for non-existent function complete_pio

complete_pio ceased to exist in commit
7972995b ("KVM: x86 emulator: Move
string pio emulation into emulator.c"), but the prototype remained.
Remove its prototype.
Signed-off-by: Josh Triplett <josh@joshtriplett.org>
Signed-off-by: Gleb Natapov <gleb@redhat.com>

arch/x86/include/asm/kvm_host.h

@@ -936,7 +936,6 @@ void kvm_mmu_new_cr3(struct kvm_vcpu *vcpu);
 void kvm_enable_tdp(void);
 void kvm_disable_tdp(void);
 
-int complete_pio(struct kvm_vcpu *vcpu);
 bool kvm_check_iopl(struct kvm_vcpu *vcpu);
 
 static inline gpa_t translate_gpa(struct kvm_vcpu *vcpu, gpa_t gpa, u32 access)