bug#36395: ssh-daemon doesn't start anymore

[Jonathan Brielmaier]

Hi,

I think 46475f72ab6127e7818fdea4a0ea9cc07c60a5f4 introduced the
following problem with the ssh-daemon service:

$ herd start ssh-daemon
Missing privilege separation directory:
/gnu/store/jpkllb...-openssh-8.0p1/var/empty
Service ssh-daemon could not be started.
herd: failed to start service ssh-daemon

After running `guix pull` from
https://gitlab.com/jonsger/Guix/commit/60a91af6bcc5bf1dbdee16b537eff8a257892458
`herd start ssh-daemon` works fine again. As
/gnu/store/...-openssh.../var/empty exists then.

~Jonathan