AP_Camera: removed incorrect mavlink sends

these sends did nothing, as MAVLINK_COMM_3 is not connected to
anything. If it was connected they would be dangerous, as a blocking
serial write could cause the stabilization of a copter not to run. If
the serial port was non-blocking it would corrupt the packet.

If we needed something like this it would have to use the MAVLink
packet queueing logic we use elsewhere