Remove sidekiq worker

Story: https://www.pivotaltracker.com/story/show/82200576

Since the Email Alert API now queues received notifications from the Email Alert Service, Sidekiq is no longer needed.
I added the random sequence to ensure the integration test always generates a document that won't be locked by the `LockHandler`.
Right now I can't think of a debugging scenario where we would gain from this being sequential rather than random, but I'm happy to make the change.