Plane: Adjust AIRSPEED_STALL parameter description

Corrected the AIRSPEED_STALL parameter description, which stated that it
was an indicated airspeed. More accurately, according to its TECS
implementation and in line with the other airspeed parameters, it is a
true airspeed (or an indicated airspeed at sea level).

Author: rubenp02

ArduPlane/Parameters.cpp

@@ -323,7 +323,7 @@ const AP_Param::Info Plane::var_info[] = {
 
     // @Param: AIRSPEED_STALL
     // @DisplayName: Stall airspeed
-    // @Description: If stall prevention is enabled this speed is used to calculate the minimum airspeed while banking. If this is set to 0 then the stall speed is assumed to be the minimum airspeed speed. Typically set slightly higher then true stall speed. Value is as an indicated (calibrated/apparent) airspeed.
+    // @Description: If stall prevention is enabled this speed is used to calculate the minimum airspeed while banking. If this is set to 0 then the stall speed is assumed to be the minimum airspeed speed. Typically set slightly higher then true stall speed.
     // @Units: m/s
     // @Range: 5 75
     // @User: Standard