Remove --offline from commands that don't realize anything and don't query remote resources

[roberth]

Describe the bug

CLI help should be relevant

Steps To Reproduce

Expected behavior

Only show relevant options

nix-env --version output

Additional context

Add any other context about the problem here.

Priorities

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[edolstra]

I think this should remain a global flag. It would be pretty painful to enumerate exactly what commands might access the network. And it doesn't really help the user in any way, since these flags are already listed separately in the manpages.

Also, making global flags non-global means you can't write stuff like this in a script:

extraNixOptions="-v"

if [[ some condition ]];
  extraNixOptions+=" --offline"
fi

nix $extraNixOptions some-command ...
nix $extraNixOptions some-other-command ...

since some of these options would no longer be accepted by all commands.

[roberth]

I think it'd be ok to just hide it from the docs, and on a best-effort basis, so no huge whitelist.

Looks like I mislabeled this, sorry about that, but I see you've fixed it.