Don't remove the key when job is executed

[kukicola]

Let's consider a case:

• job A is added to the schedule set and debounce key is created in redis
• job A is taken from schedule set and pushed to queue (and due to long queue it's waiting there)
• job B is added to the schedule set and new debounce key is created
• job A is processed and middleware removed debounce key created by job B
• job C is added to the schedule set and since debounce key was removed it won't be merged with job B

To fix that, we can keep debounce keys in redis and let them be removed automatically. Lua scripts checks if a job that is in debounce key exists in schedule set so it shouldn't lead to any problems