Remove ChefDK’s Omnitruck JSON

Now that https://github.com/opscode-cookbooks/opscode-ci/pull/149 has been merged we no longer need to maintain build -> test platform mappings in multiple locations. The pipeline’s build to test matrix is now the single source of truth. Once the Chef pipelines have been fully migrated over to the Manhattan cluster in new CI we can also remove: `jenkins/release.rb`.

This change has been fully tested in CI also:
http://manhattan.ci.opscode.us/job/chefdk-trigger-ad_hoc/173/downstreambuildview/

/cc @opscode/release-engineers @opscode/client-eng