As you wrote in your original post : How do I remove it permanently?
An article : iCloud: Delete a calendar
When you delete a calendar from your Calendars list, all events associated with the calendar are also deleted.
You can’t delete all of the calendars in the list because it must always contain at least one calendar.
WARNING: When you delete a calendar, it’s deleted from every device that has the iCloud Calendar feature turned on. For example, if your iPhone and Mac have iCloud Calendar turned on and you delete a calendar in the Calendar app on iCloud.com, the calendar is also deleted in the Calendar app on your iPhone and Mac.
Follow the steps in the article .