code: def delete(self, deviceId, measurementId):
          
          record = self.measurements.get(deviceId)
          if record is not None:
              popped = record.pop(measurementId, None)
              return popped, 200 if popped else 400
          return None, 400
docs: Deletes a stored measurement.
          :param deviceId: the device to measure.
          :param measurementId: the name of the measurement.
          :return: 200 if it was deleted, 400 if no such measurement (or device).