Ancient spirits spawned due to Aporkalypse stay if one reloads their save

Stuff spawned through the Aporkalypse is given a tag "aporkalypse_cleanup", which makes it for removal when the aporkalypse ends. This tag is not saved when saving & loading a world.

This means that every dungeon in the WORLD is permanently stuck with ghosts if you ever reload your save (usually to fix performance) after the aporkalypse starts.