systemd 246 started baking in some strings into $lib/lib/libsystemd.so
which points back to $out.
It might be desirable to not have these strings in there, but instead
have systemd ask the running manager for the really active paths via
IPC, or patch in some more mutable paths (like /run/current-system/…) -
but as long as it is as it is, we should probably should just stop
producing the `lib` output for now.
This does increase the runtime closure for installations not pulling in
systemd.out, or linking against multiple libsystemd's, but doesn't
increase the runtime closure for NixOS itself, as it needs systemd
anyways, and doesn't link against multiple variants of it.
We can also remove the aarch64-specific $out/lib/systemd/catalog hack,
and revive it at a later time if the `lib` output is reintroduced.
b68bddfbda