The URL for unregistering a webhook is the same as for registering. However, you need to use the HTTP DELETE method.
URL= https://api.sandbox.orcid.org/0000-0002-7465-2162/webhook/https%3A%2F%2Fnowhere2.com%2F0000-0002-7465-2162%2Fupdated HEADER: Authorization: Bearer [Your access token] HEADER: Content-Length: 0 METHOD: DELETE
The response should be
204 No Content.
HTTP/1.1 204 No Content Server: Apache-Coyote/1.1 Date: Fri, 05 Apr 2013 12:49:17 GMT