all appeals back to their original queues

[eviljeff]

Fixes: mozilla/addons#15439

Description

Removes the special handling for extension appeals, so rather than going into the escalations queue directly, they go back into the original queue for that entity (amo_listings) - which is how extension appeals originally worked, and non-extension appeals continued to work.

Context

I didn't entirely revert #22851 because there was some useful refactoring in there, and I wanted to leave open the possibility that we may want to target different queues for appeals again in the future.

Testing

• (you need your Cinder API key defined)
• report an extension for abuse (anything but policy violation in the addon/both)
• make a decision on the extension in Cinder (amo dev listings)
• play back the payload locally, so you have the ContentDecision instance and the email in django admin fake mail
• use the appeal link in the fake mail to appeal
• see the appeal job is in the amo dev listings queue, rather than escalations

Checklist

• Add #ISSUENUM at the top of your PR to an existing open issue in the mozilla/addons repository.
• Successfully verified the change locally.
• The change is covered by automated tests, or otherwise indicated why doing so is unnecessary/impossible.
• Add before and after screenshots (Only for changes that impact the UI).
• Add or update relevant docs reflecting the changes made.