As far as I see, any created "Quick Delivery" task with own original schedule (not shared schedule) has schedule in "Task Scheduler Library" and each schedule contains name mention about this "Quick Delivery" task, so if you are 100% sure, that this "Quick Delivery" task is deleted from SMP Console, then you can manually delete its schedule from "Task Scheduler Library".
Otherwise, if you've manually removed schedule from "Task Scheduler Library", but "Quick Delivery" still remains in SMP Console, then it will not be executed on schedule.
Note:
- I can say that after deletion of "Quick Delivery" task on ITMS 7.5 HF6, it successfully removes this schedule from "Task Scheduler Library" as well as from SMP Console.
- If you're deleting a "Quick Delivery" task from Console, but its schedule remains in "Task Scheduler Library", it looks like an issue.