Deletes a custom property from a report element.
DELETE /documents/<documentID>/reports/<reportID>/elements/<elementID>/properties/<propertyKey>
Response type: application/xml or application/json
The response is a message stating the success or failure of the request.
DELETE /documents/1234/reports/1/elements/100/properties/MYKEY
<success> <message>The resource of type "Property" has been successfully removed.</message> <id>MYKEY</id> </success>