This takes another pass over the modern services to remove unused code. I switched the shared code to use a function instead of a class and removed the indirection in the route params which led to skew between the route and examples and wasn't making things any clearer.
This will definitely save time, and ensure more uniformity.
It moves the `createServiceTester()` calls to a different place from where I'd like them, though I'm happy to have them checked by the linter.
Closes#2701
Fixes#2876 with @paulmelnikow's suggestion
Moved imports of `ServiceTester` and `createServiceTester` to a separate file so that dev dependencies are not imported by service classes.
Continue to implement #2698:
- Add `core/base-service/index.js` (but hold off on moving the things it imports)
- Add shortcuts in `services/index.js` for Base*Service, errors, and deprecatedService. This file will be streamlined later to avoid cluttering it with rarely used bits.
- Apply consistent ordering of imports and use of `module.exports` in testers.
- Remove some renaming of imports.
- Remove obsolete tests here and there.
