Launch detector: Use idle throttle param

src/lib/launchdetection/LaunchDetector.cpp

@@ -48,7 +48,7 @@ LaunchDetector::LaunchDetector() :
 	SuperBlock(NULL, "LAUN"),
 	activeLaunchDetectionMethodIndex(-1),
 	launchdetection_on(this, "ALL_ON"),
-	throttlePreTakeoff(this, "THR_PRE")
+	throttlePreTakeoff(nullptr, "FW_THR_IDLE")
 {
 	/* init all detectors */
 	launchMethods[0] = new CatapultLaunchMethod(this);

src/lib/launchdetection/launchdetection_params.c

@@ -77,7 +77,7 @@ PARAM_DEFINE_FLOAT(LAUN_CAT_T, 0.05f);
  * Motor delay
  *
  * Delay between starting attitude control and powering up the throttle (giving throttle control to the controller)
- * Before this timespan is up the throttle will be set to LAUN_THR_PRE, set to 0 to deactivate
+ * Before this timespan is up the throttle will be set to FW_THR_IDLE, set to 0 to deactivate
  *
  * @unit seconds
  * @min 0
@@ -97,14 +97,3 @@ PARAM_DEFINE_FLOAT(LAUN_CAT_MDEL, 0.0f);
  * @group Launch detection
  */
 PARAM_DEFINE_FLOAT(LAUN_CAT_PMAX, 30.0f);
-
-/**
- * Throttle setting while detecting launch.
- *
- * The throttle is set to this value while the system is waiting for the take-off.
- *
- * @min 0
- * @max 1
- * @group Launch detection
- */
-PARAM_DEFINE_FLOAT(LAUN_THR_PRE, 0.0f);