message: docs: remove AngularDart from the version picker
  At this point it's only confusing people.
  PR Close
diff: { "title": "v6", "url": "https://v6.angular.io" },
  { "title": "v5", "url": "https://v5.angular.io" },
  { "title": "v4", "url": "https://v4.angular.io" },
  - { "title": "v2", "url": "https://v2.angular.io" },
  - { "title": "AngularDart", "url": "https://webdev.dartlang.org/angular" }
  + { "title": "v2", "url": "https://v2.angular.io" }
  ]
  }
  