code: def deactivate_mfa_device(self, user_name, serial_number):
          
          params = {'UserName' : user_name,
                    'SerialNumber' : serial_number}
          return self.get_response('DeactivateMFADevice', params)
docs: Deactivates the specified MFA device and removes it from
          association with the user.
  
          :type user_name: string
          :param user_name: The username of the user
          
          :type serial_number: string
          :param seriasl_number: The serial number which uniquely identifies
                                 the MFA device.