Only look up private toots from database if the request failed because of 401,
403 or 404 errors, as those may indicate a private toot, rather than something
that isn't a toot or cannot be processed.
* Remove “protocol” argument and return value, as only ActivityPub is supported
* Remove FetchRemoteAccountService, only use ActivityPub::FetchRemoteAccountService
* Fix tests
Eugen Rochko