sound: Remove hw.snd.version and SND_DRV_VERSION

hw.snd.version and SND_DRV_VERSION define the sound driver version and
are meant to be used in bug reports, but because these values are
constant, there is not much useful information we can extract from them.

Sponsored by: The FreeBSD Foundation
MFC after: 1 week
Reviewed by: dev_submerge.ch, emaste
Differential Revision: https://reviews.freebsd.org/D44996

(cherry picked from commit 7398d1ece5cfa2e6ce4997234a95115b49c9e818)