Remove the OSS support for OpenBSD. The OSS API has not been usable
for quite some time.

Signed-off-by: Brad Smith <brad@comstyle.com>
Reviewed-by: Laszlo Ersek <lersek@redhat.com>
Reviewed-by: Andreas Färber <afaerber@suse.de>
Signed-off-by: Blue Swirl <blauwirbel@gmail.com>