sound: Retire unused emu10k1-mkalsa.sh

It is a legacy script which is no longer used. Its utility is also
unknown.

Sponsored by: The FreeBSD Foundation
MFC after: 1 week
Reviewed by: markj
Differential Revision: https://reviews.freebsd.org/D56043

(cherry picked from commit 71c46c8c901be2a6e0708c912f0d766d49e5b335)