KVM: SVM: Drop unused AVIC / kvm_x86_ops declarations

Drop a handful of unused AVIC function declarations whose implementations
were removed during the conversion to optional static calls.

No functional change intended.

Fixes: abb6d479 ("KVM: x86: make several APIC virtualization callbacks optional")
Signed-off-by: Sean Christopherson <seanjc@google.com>
Message-Id: <20220614230548.3852141-2-seanjc@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>