Remove usage of `Makefile` in production environment

The `dotcom-rendering/Makefile` is here to provide developer convenience.

In its current state, it is also used to start production scripts, with confusingly similar names:
- `start`
- `start-prod`
- `start-ci`

This means that if any file required by these commands is missing from the riff-raff artifact, the server will fail to start and enter an infinite unhealthy loop.

As we do not need the convenience of checking whether Node is available and on the correct version, or any of the DevX benefits brought about by the Makefile on the production servers, we should remove all non-development (prod, ci) tasks from the Makefile, only using it for local development and using an alternative solution for production tasks (e.g. start-prod).