Newer versions of qubes-dom0-update will spawn
qubes-download-dom0-updates.sh in an xterm if GUI mode is enabled.
Therefore, we don’t need to spawn our own progress bar.
Resolves issue where the dom0 rpm database does not get used on
successive calls to qubes-dom0-update for debian updatevms.
Also resolves "cannot remove .rpmdbold.####" occurrences.
qubesos/qubes-issues#6124