[3.0] Strip code from production builds

With #159 merged, this changes how we bring in the deprecation handling code and the app's config. Previously the broccoli logic in index.js would make sure to not ship that code in prod builds, but this seems to be missing now!

Likely we should update the generated code in `app/deprecation-workflow.js` to make use of the capabilities of `@embroider/macros` to do so!