Updated admin removal for packages: using the flag on the action

[isoos]

• Fixes Package deletion admin action should just remove packages from public bucket #8730 following the pattern of Updated admin removal for package versions: using the flag on the action #8788
• follows the same admin action pattern as the moderate actions
• reuses most of the update code with moderating and deleting a package
• updated tests with only a few relevant bits, we won't need to duplicate everything, as the main code will be already tested with the moderation action
• does the actual deletion after 2 months