OpenSSH: Regen config.h for DSA retirement

The net result of this change is the removal of a few comments from
config.h; it has no direct user-facing impact as DSA was already
disabled as of commit 0b707d5fe8b6 ("ssh: Disable support for DSA
keys").

Reviewed by: jlduran, philip
Sponsored by: The FreeBSD Foundation
Differential Revision: https://reviews.freebsd.org/D49739