Before, the openssh server tried to chroot. The startup always aborted
after that, as our chroot stub currently simply returns -1. Luckily we
can use unveil instead.
Furthermore the missing ssh_host_ed25519_key also prevented the server
from successfully starting.
The previous ReadMe.md entry about socketpair missing was already
resolved by #6705.
All of these patches did the same thing, which is already in upstream
config.sub.
With this change, we need only add `use_fresh_config_sub=true` to
the package.sh file.
Note that this is not done automatically in case the port has a modified
config.sub file.
As of 8dd11ae, we have `/dev/tty`, which is used by openssh's built-in
read_passphrase function to access the TTY, making our patch
unnecessary.
Removing it also fixes a subtle issue: we did not handle the case of
stdout not being a TTY correctly, so prompts failed to show up when e.g.
the ssh process was being piped to. This made `git clone` not work when
the server's fingerprint was not already verified.
