This cleanup aims to fix a build failure:
https://travis-ci.org/rails/rails/jobs/3515951/#L482

Since travis always have both ENV vars set to "test", a test is failing
where it's expected to output the default env "development", but "test"
is the result due to RACK_ENV being set when we expect it to not be.

By cleaning this duplication we ensure that changing any of these env
variables will pick the right expected value.