target/i386: Remove unused KVM stubs

All these functions:

 - kvm_arch_get_supported_cpuid()
 - kvm_has_smm(()
 - kvm_hyperv_expand_features()
 - kvm_set_max_apic_id()

are called after checking for kvm_enabled(), which is
false when KVM is not built. Since the compiler elides
these functions, their stubs are not used and can be
removed.

Inspired-by: Daniel Henrique Barboza <dbarboza@ventanamicro.com>
Signed-off-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Message-ID: <20230904124325.79040-7-philmd@linaro.org>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>