Fix orphan loop, remove 'antimessage' references

We don't want to add the orphan id to handled_ids immediately upon
deleting the message, since that will prevent us from doing anything
with it later.

Remove some unused variables.

Reluctantly remove references to antimessages.

TODO: replacement sci-fi terminology

Bug: T99018
Change-Id: I997d73ffc833f93582fc43cec461dd8787150363