ArduCopter: remove RTL_LAND parameter as it's been deprecated in favour of APPROACH_ALT.

Updated comments on ALT_HOLD_RTL and APPROACH_ALT to make it a little easier to understand.

ArduCopter/Parameters.h

@@ -106,10 +106,9 @@ public:
 	k_param_ch7_option,
 	k_param_auto_slew_rate,
 	k_param_sonar_type,
-	k_param_super_simple,
-	k_param_rtl_land_enabled,	// Depricated!!
-	k_param_axis_enabled,
-	k_param_copter_leds_mode, //158
+	k_param_super_simple = 155,
+	k_param_axis_enabled = 157,
+	k_param_copter_leds_mode,
     k_param_ahrs,  // AHRS group
 
 	//
@@ -228,7 +227,6 @@ public:
     AP_Int8		optflow_enabled;
 	AP_Float	low_voltage;
 	AP_Int8		super_simple;
-	AP_Int8		rtl_land_enabled;
 	AP_Int16	rtl_approach_alt;
 	AP_Int8		tilt_comp;
 	AP_Int8		axis_enabled;

ArduCopter/Parameters.pde

@@ -28,8 +28,8 @@ const AP_Param::Info var_info[] PROGMEM = {
 	GSCALAR(serial3_baud,	"SERIAL3_BAUD",     SERIAL3_BAUD/1000),
 
 	// @Param: ALT_HOLD_RTL
-	// @DisplayName: Alt Hold RTL
-	// @Description: This is the altitude the model will move to before Returning to Launch
+	// @DisplayName: RTL Altitude
+	// @Description: This is the altitude the model will move to before Returning to Launch.  Set to zero to return at current altitude.
 	// @Units: Meters
 	// @Range: 0 400
 	// @Increment: 1
@@ -89,17 +89,9 @@ const AP_Param::Info var_info[] PROGMEM = {
 	// @User: Standard
 	GSCALAR(super_simple,	"SUPER_SIMPLE",     SUPER_SIMPLE),
 
-	// @Param: RTL_LAND
-	// @DisplayName: RTL Land
-	// @Description: Setting this to Enabled(1) will enable landing after RTL. Setting this to Disabled(0) will disable landing after RTL.
-	// @Values: 0:Disabled,1:Enabled
-	// @User: Standard
-	// @ DEPRICATED
-	GSCALAR(rtl_land_enabled,	"RTL_LAND",     0),
-
 	// @Param: APPROACH_ALT
-	// @DisplayName: Alt Hold RTL
-	// @Description: This is the altitude the vehicle will move to before Returning to Launch
+	// @DisplayName: RTL Approach Altitude
+	// @Description: This is the altitude the vehicle will move to as the final stage of Returning to Launch.  Set to zero to land.
 	// @Units: Meters
 	// @Range: 1 10
 	// @Increment: .1