* Remove obsolete RSS::Serializer test
Since #17828, RSS::Serializer no longer has specific code for deleted statuses,
but it is never called on deleted statuses anyway.
* Rename erroneously-named test files
* Fix failing test
* Fix test deprecation warnings
* Update CircleCI Ruby orb
1.4.0 has a bug that does not match all the test files due to incorrect
globbing
* Improve RSS entries for statuses
- Render polls in both accounts and tags serializers
- Refactor RSS serializers
- Change title preview to include ellipsis when truncated
- Change title preview to show CW instead of toot text
- Add tests
* Remove title from OEmbed serialization
Twitter doesn't serialize title either, and tihs allows us to move the
title formatting code to the RSS serializers.
Claire