AP_TECS: fixed throttle demand on underspeed

thanks to Philipp Oettershagen for finding this bug!

libraries/AP_TECS/AP_TECS.cpp

@@ -455,7 +455,7 @@ void AP_TECS::_update_throttle(void)
     // If underspeed condition is set, then demand full throttle
     if (_underspeed)
     {
-        _throttle_dem_unc = 1.0f;
+        _throttle_dem = 1.0f;
     }
     else
     {

libraries/AP_TECS/AP_TECS.h

@@ -206,9 +206,6 @@ private:
     // climbout mode
     enum FlightStage _flight_stage;
 
-	// throttle demand before limiting
-	float _throttle_dem_unc;
-
 	// pitch demand before limiting
 	float _pitch_dem_unc;