RPi fix: Make running retrievecontentpack download NOT update the DB

[benjaoming]

Summary

Before, we called update_stage, which would write progress to the DB. A pretty bad idea.

On RPi, it basically meant it was impossible to run retrievecontentpack in some cases.

Thanks @holta for reporting this!

TODO

If not all TODOs are marked, this PR is considered WIP (work in progress)

• Has documentation been written/updated?
• Have you written release notes for the upcoming release?

Reviewer guidance

I know this isn't necessarily nicely done or follows through with any kind of consequence for other commands, but this fixes the immediate issue for RPi.

Issues addressed

#5575
#4892