This completely removes client-side support for the SSH 1 protocol,
which was already disabled in 12 but is still enabled in 11. For that
reason, we will not be able to merge 7.6p1 or newer back to 11.
branch but never merged to head. They were inadvertantly left out when
6.1p1 was merged to head. It didn't make any difference at the time,
because they were unused, but one of them is required for DNS-based host
key verification.
Approved by: re (blanket)