system-helper: Fix crashes in progress callbacks when pulling
system-helper: Fix crashes in progress callbacks when pulling

I got weird crashes in the local repo pull case where the default
progress reporting callback tried to get some unset key on
the progress. We don't want any progress reporting anyway, so fix
this by dropping all progress reporting.

Closes: #1243
Approved by: alexlarsson

handsome-feng/flatpak,handsome-feng/flatpak,matthiasclasen/flatpak,matthiasclasen/flatpak,matthiasclasen/flatpak,matthiasclasen/flatpak,handsome-feng/flatpak,flatpak/flatpak,flatpak/flatpak,flatpak/flatpak,handsome-feng/flatpak,matthiasclasen/flatpak,handsome-feng/flatpak,flatpak/flatpak,flatpak/flatpak