Denying an appeal on Listing Content Rejection should drop requested

[eviljeff]

Fixes: mozilla/addons#16108

Description

Removes the requested status for content review if we deny their appeal - so the add-on no longer shows up in the reviewer tools queue.

Context

Testing

STR from the issue:

• Reject listing content for an addon
• As the owner of the addon send an appeal
• See the add-on is in the content review queue
• As a reviewer select the appeal from dsa section + deny appeal
• The add-on shouldn't be in the content review queue any longer

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.

[eviljeff]

I know I could optimize this query to be an exists, as we're only interested in one case. I just kept it the same as we do in ContentActionTargetAppealApprove so it's understandable as the same concept. But I can rewrite if you prefer? (as with the unnecessary return None at the end of the function)