x86/kvm/hyper-v: don't recommend doing reset via synthetic MSR

System reset through synthetic MSR is not recommended neither by genuine
Hyper-V nor my QEMU.

Fixes: 2bc39970 ("x86/kvm/hyper-v: Introduce KVM_GET_SUPPORTED_HV_CPUID")
Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com>
Reviewed-by: Liran Alon <liran.alon@oracle.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>