code: def unlink(self):
          
          s_line_obj = self.env['sale.order.line']
          for line in self:
              if line.service_line_id:
                  sale_unlink_obj = s_line_obj.browse([line.service_line_id.id])
                  sale_unlink_obj.unlink()
          return super(HotelServiceLine, self).unlink()
docs: Overrides orm unlink method.
          @param self: The object pointer
          @return: True/False.