clean-system script removes turned off distroboxes

[wolfyreload]

Looking at the clean-system script, the podman system prune -a command removes all containers that are off which makes this a rather dangerous and destructive. I ran it and nuked my distrobox dev environment accidentally. Also the confirmation dialog might be confusing for new users.

I propose switching to a safer script that just removes unused podman images and volumes as this is typically safe. If you want to remove turned off containers I'd rather leave that up to the end user to do manually