Unexport switch_to_{hv,sw}_timer() now that common x86 handles the
transitions.

No functional change intended.
Signed-off-by: NSean Christopherson <seanjc@google.com>
Reviewed-by: NMaxim Levitsky <mlevitsk@redhat.com>
Message-Id: <20211208015236.1616697-9-seanjc@google.com>
Signed-off-by: NPaolo Bonzini <pbonzini@redhat.com>