This reverts commit e2675f57b5f747b6a9e21067c75911fbd0341943.
This reverts commit 4946b6b296.
4946b6b296
* Implement a ViewedEvent handling system which calls handlers when a block has been viewed for 5 seconds (configurable). * Hook up Verticals to register their children blocks with this event, and submit completions once seen. OSPR-2093 OC-3358