Remove CONTRIBUTING.md file
Remove CONTRIBUTING.md file

We don't get external contributions and this file is confusing, inconsistent, noise.

https://trello.com/c/iYNuFHCm/259-remove-contributingmd-files-from-repos

alphagov/govuk-puppet,alphagov/govuk-puppet,alphagov/govuk-puppet,alphagov/govuk-puppet,alphagov/govuk-puppet,alphagov/govuk-puppet