audio: remove plive

It was useless even 3 years ago, so it can probably safely go away:
https://lists.nongnu.org/archive/html/qemu-devel/2012-03/msg02427.html



Signed-off-by: Kővágó, Zoltán <DirtY.iCE.hu@gmail.com>
Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>