AP_NavEKF3: remove unused EK3_GSF_DELAY param

libraries/AP_NavEKF3/AP_NavEKF3.cpp

@@ -614,15 +614,7 @@ const AP_Param::GroupInfo NavEKF3::var_info[] = {
     // @RebootRequired: True
     AP_GROUPINFO("GSF_USE_MASK", 58, NavEKF3, _gsfUseMask, 3),
 
-    // @Param: GSF_DELAY
-    // @DisplayName: Delay from loss of navigation to yaw reset
-    // @Description: If the inertial navigation calculation stops following the GPS and other positioning sensors for longer than EK3_GSF_DELAY milli-seconds, then the EKF3 code will generate a reset request internally and reset the yaw to the estimate from the EKF-GSF filter and reset the horizontal velocity and position to the GPS. This reset will not be performed unless the use of the EKF-GSF yaw estimate is enabled via the EK3_GSF_USE parameter.
-    // @Range: 500 5000
-    // @Increment: 100
-    // @Units: ms
-    // @User: Advanced
-    // @RebootRequired: True
-    AP_GROUPINFO("GSF_DELAY", 59, NavEKF3, _gsfResetDelay, 1000),
+    // 59 was GSF_DELAY which was never released in a stable version
 
     // @Param: GSF_RST_MAX
     // @DisplayName: Maximum number of resets to the EKF-GSF yaw estimate allowed

libraries/AP_NavEKF3/AP_NavEKF3.h

@@ -417,7 +417,6 @@ private:
     AP_Int16 _mag_ef_limit;         // limit on difference between WMM tables and learned earth field.
     AP_Int8 _gsfRunMask;            // mask controlling which EKF3 instances run a separate EKF-GSF yaw estimator
     AP_Int8 _gsfUseMask;            // mask controlling which EKF3 instances will use EKF-GSF yaw estimator data to assit with yaw resets
-    AP_Int16 _gsfResetDelay;        // number of mSec from loss of navigation to requesting a reset using EKF-GSF yaw estimator data
     AP_Int8 _gsfResetMaxCount;      // maximum number of times the EKF3 is allowed to reset it's yaw to the EKF-GSF estimate
     AP_Float _err_thresh;           // lanes have to be consistently better than the primary by at least this threshold to reduce their overall relativeCoreError
     AP_Int32 _affinity;             // bitmask of sensor affinity options