This is just another step toward getting what we're doing with inheritance to be a little more sane, ultimately, this may be refactored further, as I am not happy with some of these subscribers adding their own teardowns, but this is a start. The goal was to get rid of the weirdness around `_unsubscribe` in our code base.

- Moves to calling `_unsubscribe` a new internal name in `Subscription`: `initialTeardown`, because it's slightly more descriptive
- Removes `_unsubscribe` usage from the entire codebase.
- Formatted a few files just for my sanity.