Cancel queued publishing jobs when undoing an activity

I've had this on my backlog for ages. We track deliveries, so if we cancel these jobs before initiating the federation of a Delete, Unrepeat, Unfavorite, etc it will help avoid wasting resources and the e.g., Delete will be federated to fewer servers. This is most evident when someone quickly deletes/unboosts/unfavs a post after the original action.

• Create post, delete post. Undelivered jobs are cancelled.
• Boost post, unboost post. Undelivered jobs are cancelled.
• Favorite post, unfavorite post. Undelivered jobs are cancelled.
• React to post, unreact to post. Undelivered jobs are cancelled.