openssh: retire client VersionAddendum option handling

[emaste]

Summary

Client-side VersionAddendum support was removed from base system SSH in
April 2022, in commit bffe60ead024.  We retained the option parsing
(using OpenSSH's support for deprecated options) to avoid breaking
existing installations upon upgrade, but sufficient time has now passed
that we can remove this special case.

Relnotes:       Yes
Sponsored by:   The FreeBSD Foundation

[emaste]

(Not to be committed until sufficient time has actually passed - after stable/14 branch, perhaps.)

[emaste]

(and update crypto/openssh/FREEBSD-upgrade when this goes in)