[Chore] Remove WatchdogPlugin.getInstance()

[adamk33n3r]

This makes things harder to test. It should be injected everywhere it's needed. And really, most of the time it's just used as a central repository for things I don't want to have to inject like gson, the config, etc. It was nice to iterate fast, but as this codebase is becoming more mature, adding tests would be nice and it's a PITA when nested code is just calling this.