Causes duplicate jobs to be created on restart

[adambutler]

We were using version 1.0.0.alpha.1 with Sidekiq 5.5.9 when we noticed a strange issue where we would get many copies of jobs in our retry queue.

We upgraded sidekiq to 7.1.2 but the issue persisted and could be reliably replicated until we removed sidekiq-throttled.

Steps to replicate:

1. Queue a job that will raise in our case this job was not using sidekiq-throttled
2. Allow it to go into the retry queue
3. Restart the sidekiq process
4. Many copies of the job get created

Whilst investigating we removed this dependency and the issue stopped presenting itself.