lorder: add deprecation notice

lorder has not been used by the base system since 0e1e341b486c and
hasn't really been necessary for a very long time.

PR: 259254 [exp-run]
Reviewed by: arichardson (earlier)
Sponsored by: The FreeBSD Foundation
Differential Revision: https://reviews.freebsd.org/D30080

(cherry picked from commit 68a930d8ee35dd6ecc16254667a07e5be0a6f841)