Remove the audio-path drivers (IRIG and CHU) and their support/test code.

Our PM says: "Kill all audio path drivers.  It was a cute stunt back
when hobbylab machines had audio frequency specialized sound cards but
didn't have general gpio/sdr/dsp inputs. Nobody actually serious would
use them now." Tech lead concurs.  This gets rid of a lot of auxiliary
cruft that was lurking in cobwebby corners.