Filters: episodes from unsubscribed podcasts added to the Unplayed filter

Initially reported in [5201571-zen](https://woothemes.zendesk.com/agent/tickets/5201571) and continued discussion on Slack: p1652147666837189-slack-C02A333D8LQ

> This is the second time now I’ve launched the app and noticed a feed that I’m not subscribed to is populating one of my filters.
The podcast is called Prestige TV and it’s showing up in my Unplayed filter. I’m not able to interact with any of the episodes in the filter list, and last time this happened I had to search for the podcast from Discover -> subscribe -> unsubscribe to clear the episodes out of my filter.

On May 12, it happened again but added other different podcast episodes to the filter:

https://user-images.githubusercontent.com/40906847/167990654-0793c81e-01ab-4e4b-aae2-e6eab73c6c67.MOV

App Version: 7.20
Device: iPhone14,2
OS: 15.5

No source file, test, or entry point is identified. Reproduce the issue using the reported iPhone 14,2, iOS 15.5, and app version 7.20, then trace how the Unplayed filter handles subscription state. Done means episodes from unsubscribed podcasts no longer appear in the filter and existing stale entries can be cleared without resubscribing.

Written by the indexing model from the issue text.