Deleting a calendar in iCloud ensures that the subscription is removed from each device that is linked to that iCloud account. eg. If your Desktop and Mobile both have iCloud activated and you delete a calendar from the Calendar App on the device, it maybe come back via iCloud. To remove the subscription entirely, follow these steps:

1. Go to https://www.icloud.com/
2. Log in with your Apple ID credentials
3. Click on the “Calendar’ Icon
4. In the left hand column, locate the ECAL Calendar that you are subscribed to
5. Click Edit at the top of the Calendar list.
6. Click the Delete button to the right of the calendar’s name, then click Delete.