EKF: do not fuse multiple times the same height (#767)

* EKF: do not fuse multiple times the same height

The _fuse_height flag was never set to zero, hence the fusion was called
at each iteration, even if no new data is available.
The effects were: high CPU usage and virtually less measurement noise
due to multiple fusion of the same sample

Also remve unused variables

EKF/vel_pos_fusion.cpp

@@ -139,7 +139,7 @@ bool Ekf::fuseVerticalPosition(const Vector3f &innov, const Vector2f &innov_gate
 // Helper function that fuses a single velocity or position measurement
 void Ekf::fuseVelPosHeight(const float innov, const float innov_var, const int obs_index) {
 
-	float Kfusion[24] = {};  // Kalman gain vector for any single observation - sequential fusion is used.
+	float Kfusion[24];  // Kalman gain vector for any single observation - sequential fusion is used.
 	const unsigned state_index = obs_index + 4;  // we start with vx and this is the 4. state
 
 	// calculate kalman gain K = PHS, where S = 1/innovation variance