Remove the conditional for precompiling assets in Dockerfile
Remove the conditional for precompiling assets in Dockerfile

As part of the work to use the built images pushed up to Docker Hub for
E2E testing, where we run the tests in the production RAILS_ENV, we will need
the image pushed up to contain the compiled assets.

We can't see a reason to keep the conditional for now as any performance
hit will be experienced only as part of CI.

alphagov/manuals-publisher,alphagov/manuals-publisher,alphagov/manuals-publisher