gitlab-lint: Drop since available tokens are not enough

After the GitLab "Unauthenticated CI lint API may lead to information disclosure and SSRF" fix shipped with version 13.8.4 the ci/lint endpoints requires authentication but:

1. $CI_JOB_TOKEN is not enough
2. $TEST_GITLAB_AUTH_TOKEN is not enough either, some extra permissions are required

Given that the YAML will get tested anyway when trying to trigger real pipelines on the scratch tests/dash> repository, let's just drop the lint CI job rather than granting more permissions than necessary.