Copter: move serial_control case to base class

ArduCopter/GCS_Mavlink.cpp

@@ -1558,10 +1558,6 @@ void GCS_MAVLINK_Copter::handleMessage(mavlink_message_t* msg)
         break;
     }
 
-    case MAVLINK_MSG_ID_SERIAL_CONTROL:
-        handle_serial_control(msg, copter.gps);
-        break;
-
 #if PRECISION_LANDING == ENABLED
     case MAVLINK_MSG_ID_LANDING_TARGET:
         result = MAV_RESULT_ACCEPTED;