No one references kvm_check_extension, kvm_has_vcpu_events, and
kvm_has_robust_singlestep outside KVM code.

kvm_update_guest_debug is never called, thus has no job besides
returning an error.
Signed-off-by: NJan Kiszka <jan.kiszka@siemens.com>
Signed-off-by: NMarcelo Tosatti <mtosatti@redhat.com>