You can delete a document referenced by its ID.
DELETE <webiURL>/documents/{documentId}/links/{linkId}
Where:
Response type: application/xml or application/json
The response is a message stating the success or failure of the request.
DELETE <webiURL>//documents/8022/links/L4
<success> <message>The resource of type 'Link' with identifier 'L4' has been successfully removed.</message> <id>L4</id> </success>