25112117

By: Tom Sydney Kerckhove <syd@cs-syd.eu>

Check the lease commands harder, and rip out what nothing uses

The leases are in the half a reset is paired with now, so a lease line
that will not take costs the whole of it. Two checks that were not worth
much when they only cost the second half:

A lease naming a dhcp server nothing here creates. Unlike an interface, a
dhcp server is never hardware: a name a file does not create does not
exist anywhere.

A lease for an address no server here hands out, which is a lease nothing
can ever be given.

The test that was supposed to prove a missing half stops a deployment was
passing for the wrong reason: it handed apply a --checked-against that was
not the router, so the staleness gate fired first and the missing half was
never reached. It downloads the router first now, and asserts the message
names the file. The staleness gate has its own test, which asserts it
names the download and records nothing.

Ripped out: download's three separate output flags, which only the README
still used, leaving --into and one place where those three names are
decided; an unused stdenv argument, an unused pkgsMusl binding and an
unused overlay argument; and a needless borrow clippy pointed at.

deadnix and statix hooks, since those three unused things had been sitting
there and the tools that find them were not running here.