ekf: remove unused function

EKF/ekf.h

@@ -545,9 +545,6 @@ private:
 	// jacobian : 4x1 vector of partial derivatives of observation wrt each quaternion state
 	void updateQuaternion(const float innovation, const float variance, const float gate_sigma, const float (&yaw_jacobian)[4]);
 
-	// shrinks the yaw axis uncertainty of quaternion covariances by fusing a zero innovation yaw observation
-	void shrinkYawVariance();
-
 	// fuse the yaw angle obtained from a dual antenna GPS unit
 	void fuseGpsAntYaw();