Hi Guix, attached is a patch to add context to the warning about the
system field. When offloading, we get this message if we haven't
updated our machines.scm:

guix offload: warning: The 'system' field is deprecated, please use
'systems' instead.

and it's not clear what system field this message is refering to
(especially for me, since I simply re-enabled offloading after a few
months by copying my old backup machines.scm).

Now the message is:

/etc/guix/machines.scm:9:6: warning: The 'system' field is deprecated,
please use 'systems' instead.

which directs the user to the right file, and line (so if you have many
offload machines, you know where to fix).

Since the message comes from the daemon, you need to run the daemon
from your guix checkout to test the patch.