Deletes the list and every number in it, and answers 204 No Content with no body. A
number that no other list of the organization watches stops counting against the
allowance at once. The webhook endpoints that receive this list alone are deleted with
it, together with their delivery log; endpoints that receive every list are kept.
A list of another organization and an id that never existed are both 404 not_found.
Deleting is not undone: create the list again to restore it. Not counted as a call.