Remove this project, move directly into gitlab-styles

With Brian gone, I worry this project will stagnate and be forgotten. It's only in GitLab CE as a dependency-of-dependency for gitlab-styles. I'm thinking we should just move these cops directly into that gem.

WDYT @rymai?

Steps

• Move cops to gitlab-styles - gitlab-org/ruby/gems/gitlab-styles!151 (merged)
• Wait for gitlab-styles to be released
• Mention that the cops were moved to gitlab-styles in README.md - !12 (merged)
• Move issues from this repo to https://gitlab.com/gitlab-org/ruby/gems/gitlab-styles
• Mark project as read-only
• Remove project from Engineering Projects page - gitlab-com/www-gitlab-com!120440 (merged)