Update CloudIoT payload to skip header.
Update CloudIoT payload to skip header.

* The header information is not required for a MQTT upload, this
  information is seperately passed via MQTT.
* Payload is now just json.dumps of the desired message.

Change-Id: I6c049a7301d79607818fcfc04dee158a0bcd554c

google/aiyprojects-raspbian,google/aiyprojects-raspbian,google/aiyprojects-raspbian,google/aiyprojects-raspbian,google/aiyprojects-raspbian