Disabling Kanban backlog doesn't toggle the "Epic panel" off

Issue Summary

If the Kanban board doesn't have Kanban backlog enabled, the Epic Panel toggle has to be always set to off.

Steps to Reproduce

1. Create a Kanban board
2. Enable Kanban backlog and set the Epic Panel on
3. Disable Kanban backlog
4. The toggle will still be set to on in the background

Expected Results

The Epic Panel should be set to off.

Actual Results

The Epic Panel toggle remains active. 

Workaround

Enable the Kanban backlog and set the Epic Panel to off and disable the Kanban backlog afterward.