The Queues Module has an option entitled IVR Break Out Menu that causes a call to the Queue to break out to an IVR periodically.
If an IVR is selected, submitted, and applied, and then later changed to "None," the "None" option will show in the GUI, but the system will continue to function as if the prior IVR was selected.
The only way to get the IVR removed is to delete the Queue and create a new one.