sound: Retire SND_DIAGNOSTIC PCM locking macros

Disabled by default, but also redundant, since most of the errors they
catch will be caught anyway by WITNESS and the locking subsystem.

Sponsored by: The FreeBSD Foundation
MFC after: 1 week
Reviewed by: kib
Differential Revision: https://reviews.freebsd.org/D53735

(cherry picked from commit b19e61f223a1982cce103b9716568391a071892a)