AP_NavEKF2: Fix bug in flow fusion for terrain estimation

Also remove unused class variables

libraries/AP_NavEKF2/AP_NavEKF2_OptFlowFusion.cpp

@@ -188,7 +188,7 @@ void NavEKF2_core::EstimateTerrainOffset()
             losPred =   relVelSensor.length()/flowRngPred;
 
             // calculate innovations
-            auxFlowObsInnov = losPred - sqrtf(sq(flowRadXYcomp[0]) + sq(flowRadXYcomp[1]));
+            auxFlowObsInnov = losPred - sqrtf(sq(ofDataDelayed.flowRadXYcomp[0]) + sq(ofDataDelayed.flowRadXYcomp[1]));
 
             // calculate observation jacobian
             float t3 = sq(q0);
@@ -234,7 +234,7 @@ void NavEKF2_core::EstimateTerrainOffset()
             auxFlowTestRatio = sq(auxFlowObsInnov) / (sq(MAX(0.01f * (float)frontend->_flowInnovGate, 1.0f)) * auxFlowObsInnovVar);
 
             // don't fuse if optical flow data is outside valid range
-            if (MAX(flowRadXY[0],flowRadXY[1]) < frontend->_maxFlowRate) {
+            if (MAX(ofDataDelayed.flowRadXY[0],ofDataDelayed.flowRadXY[1]) < frontend->_maxFlowRate) {
 
                 // correct the state
                 terrainState -= K_OPT * auxFlowObsInnov;

libraries/AP_NavEKF2/AP_NavEKF2_core.h

@@ -926,8 +926,6 @@ private:
     bool fuseOptFlowData;           // this boolean causes the last optical flow measurement to be fused
     float auxFlowObsInnov;          // optical flow rate innovation from 1-state terrain offset estimator
     float auxFlowObsInnovVar;       // innovation variance for optical flow observations from 1-state terrain offset estimator
-    Vector2 flowRadXYcomp;          // motion compensated optical flow angular rates(rad/sec)
-    Vector2 flowRadXY;              // raw (non motion compensated) optical flow angular rates (rad/sec)
     uint32_t flowValidMeaTime_ms;   // time stamp from latest valid flow measurement (msec)
     uint32_t rngValidMeaTime_ms;    // time stamp from latest valid range measurement (msec)
     uint32_t flowMeaTime_ms;        // time stamp from latest flow measurement (msec)