EKF hotfix: Remove unused variables, use default initializer list for vectors

src/modules/ekf_att_pos_estimator/estimator_23states.h

@@ -172,8 +172,6 @@ public:
     unsigned covSkipCount; // Number of state prediction frames (IMU daya updates to skip before doing the covariance prediction
 
     // GPS input data variables
-    float gpsCourse;
-    float gpsVelD;
     double gpsLat;
     double gpsLon;
     float gpsHgt;

src/modules/ekf_att_pos_estimator/estimator_utilities.h

@@ -19,9 +19,7 @@ public:
     float y;
     float z;
 
-    Vector3f() { zero(); }
-
-    Vector3f(float a, float b, float c) :
+    Vector3f(float a=0.0f, float b=0.0f, float c=0.0f) :
     x(a),
     y(b),
     z(c)