Remove source environment.sh
Remove source environment.sh

This was previously working because, by sourcing environment.sh after
environment_test.sh, the SETTINGS env var was 'dev' instead of 'test' which
meant that the (problematic) TESTING Flask app config was not getting set.
We've now fixed digital-register-frontend to not set TESTING, meaning that
we can switch back to sourcing environment_test.sh last.

LandRegistry/centos-dev-env,LandRegistry/centos-dev-env,LandRegistry/centos-dev-env