sound: remove snddev_info->inprog and pcm_inprog()
No longer used.
Sponsored by: The FreeBSD Foundation
MFC after: 2 weeks
Reviewed by: markj
Differential Revision: https://reviews.freebsd.org/D43737
(cherry picked from commit 883b8ed582eb3e9e98c62c471228ff3c3a25377d)