You can not delete the workorder or workorder item because it was created as a result of accepting the service request and linked to that service requerst; nor can you delete the service request because a workorder item has been created when it was accepted and is linked to that workorder item.
You can edit the workorder item - i.e. delete the text that was transfered from the service request to the workorder item , but you can not delete the workorder item itself, nor delete the service request to maintain database integrity