bhnd: remove srand() to ensure deterministic output

bhnd: remove srand() to ensure deterministic output

r310342 fixed non-deterministic nvram_map_gen.awk output and thus a non-
reproducible bhnd(4) build by using a unique sort key.

Go one step further and also remove the srand() call. There's no reason
we want non-deterministic behaviour from this script.

PR:		215422
Reported by:	gjb (non-reproducibility of bhnd)
Reported by:	lidl (srand as the cause)
Reviewed by:	landonf
Sponsored by:	The FreeBSD Foundation
Differential Revision:	https://reviews.freebsd.org/D8857