There's no reason why we should keep VNC enabled when the user
specified --without-default-features.

Reported-by: Cole Robinson <crobinso@redhat.com>
Signed-off-by: Thomas Huth <thuth@redhat.com>
Message-Id: <20210713093155.677589-3-thuth@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>