fix(just): adjust clean-system script to not delete turned off distro…

…box containers (#274)

build/ublue-os-just/20-clean.just

@@ -1,8 +1,9 @@
 # vim: set ft=make :
 
-# Clean up old containers and flatpaks
+# Clean up old up unused podman images, volumes, flatpak packages and rpm-ostree content
 clean-system:
     #!/usr/bin/bash
-    podman system prune -a
+    podman image prune -af
+    podman volume prune -f
     flatpak uninstall --unused
     rpm-ostree cleanup -bm