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.
Damien Mathieu