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

msg/Airspeed.msg

@@ -5,6 +5,4 @@ float32 indicated_airspeed_m_s   # indicated airspeed in m/s
 
 float32 true_airspeed_m_s        # true filtered airspeed in m/s
 
-float32 air_temperature_celsius  # air temperature in degrees Celsius, -1000 if unknown
-
 float32 confidence               # confidence value from 0 to 1 for this sensor