"You can removed cached packages..." message is a lie

[wgwoods]

So DNF 1.1.0, at the end of the download, says:

Download complete! Use 'dnf system-upgrade reboot' to start the upgrade.
The downloaded packages were saved in cache till the next successful transaction.
You can remove cached packages by executing 'dnf clean packages'.

The first line is printed by the plugin, the latter two lines are printed by DNF itself.

But: (AFAIK) dnf clean packages actually won't remove the downloaded packages, because it doesn't know that we stashed them in our own datadir instead of the normal cachedir.

So: we should suppress this message, and/or suggest dnf system-upgrade clean instead.