This `ENV` was added to the Dockerfile in b96093fa56,
when the repository used per-architecture Dockerfiles, and some architectures needed
a different configuration.
Now that we use a multi-arch Dockerfile, and CI uses a Jenkinsfile, we can remove
this `ENV` from the Dockerfile, and set it in CI instead if needed.
Also updated the wording and fixed linting issues in hack/validate/gometalinter
Signed-off-by: Sebastiaan van Stijn <github@gone.nl>
a464a3d51f