Clean up temperature msg fields (#24272)

* remove temp field from airspeed.msg, adjust temp selection

* temp-sensor hirarchy: airspeed, ext. baro, default value

* directly use diff-press or baro temp in true-airspeed  calc

* improve clarity

* add enum for temperature source in VehicleAirData.msg

src/drivers/telemetry/hott/messages.cpp

@@ -150,7 +150,7 @@ build_eam_response(uint8_t *buffer, size_t *size)
 	msg.eam_sensor_id = EAM_SENSOR_ID;
 	msg.sensor_text_id = EAM_SENSOR_TEXT_ID;
 
-	msg.temperature1 = (uint8_t)(airdata.baro_temp_celcius + 20);
+	msg.temperature1 = (uint8_t)(airdata.ambient_temperature + 20);
 	msg.temperature2 = msg.temperature1 - BOARD_TEMP_OFFSET_DEG;
 
 	msg.main_voltage_L = (uint8_t)(battery.voltage_v * 10);

src/drivers/uavcan/sensors/airspeed.cpp

@@ -104,7 +104,6 @@ UavcanAirspeedBridge::ias_sub_cb(const
 	report.timestamp   		= hrt_absolute_time();
 	report.indicated_airspeed_m_s   = msg.indicated_airspeed;
 	report.true_airspeed_m_s   	= _last_tas_m_s;
-	report.air_temperature_celsius 	= _last_outside_air_temp_k + atmosphere::kAbsoluteNullCelsius;
 
 	publish(msg.getSrcNodeID().get(), &report);
 }