Remove Special:GettingStarted and notifications

* Productize test version from OB6
* Remove all references to the special page
* Remove all Echo notifications
* Change GettingStarted to be officially an API extension
* Remove dead code and minor fm

Bug: 54993
Bug: 54362
Bug: 48868

Change-Id: Iab6b347c6e3b1810291e2f8206fc2534dc787d02
Merge "Remove Special:GettingStarted and notifications"