With the big event at the end of January it's a good time to do some quick cleaning of banned channels out of search results. Note this is not a long term fix to the channel caching issues. It's just a quick clean up before a major event.

• Clean banned channel out of search caching so they don't appear in searches or as suggested channels.

https://minds.zulipchat.com/#narrow/stream/192978-bugs/topic/Banned.20channels.20in.20search.20results/near/184960318

changed due date to January 28, 2020

added scoped label

This is going to be for @markeharding to do because he's the only one with write access to production elastic search

assigned to @markeharding