bug#61627: Cannot start a container built with `guix system container --network'.

[Arun Isaac]

> I'm inclined to keep it in %network-configuration-files just to be
> safe.

I agree. I don't really understand the implications of removing
/etc/hosts from %network-configuration-files. I would err on the side of
caution and leave it there for now.

@Pierre: Could you make a patch of the fix you suggested earlier
(removing hosts-service-type when the --network flag is provided) and
push it? Thank you!