AP_OpticalFlow: use AHRS singleton

libraries/AP_OpticalFlow/AP_OpticalFlow_Pixart.cpp

@@ -289,7 +289,7 @@ void AP_OpticalFlow_Pixart::timer(void)
 
     uint32_t dt_us = last_burst_us - integral.last_frame_us;
     float dt = dt_us * 1.0e-6;
-    const Vector3f &gyro = get_ahrs().get_gyro();
+    const Vector3f &gyro = AP::ahrs_navekf().get_gyro();
 
     {
         WITH_SEMAPHORE(_sem);

libraries/AP_OpticalFlow/OpticalFlow.cpp

@@ -69,9 +69,7 @@ const AP_Param::GroupInfo OpticalFlow::var_info[] = {
 };
 
 // default constructor
-OpticalFlow::OpticalFlow(AP_AHRS_NavEKF &ahrs)
-    : _ahrs(ahrs),
-      _last_update_ms(0)
+OpticalFlow::OpticalFlow()
 {
     _singleton = this;
 

libraries/AP_OpticalFlow/OpticalFlow.h

@@ -30,7 +30,7 @@ class OpticalFlow
     friend class OpticalFlow_backend;
 
 public:
-    OpticalFlow(AP_AHRS_NavEKF& ahrs);
+    OpticalFlow();
 
     /* Do not allow copies */
     OpticalFlow(const OpticalFlow &other) = delete;
@@ -87,7 +87,6 @@ private:
 
     static OpticalFlow *_singleton;
 
-    AP_AHRS_NavEKF &_ahrs;
     OpticalFlow_backend *backend;
 
     struct AP_OpticalFlow_Flags {

libraries/AP_OpticalFlow/OpticalFlow_backend.h

@@ -50,9 +50,6 @@ protected:
 
     // apply yaw angle to a vector
     void _applyYaw(Vector2f &v);
-    
-    // get access to AHRS object
-    AP_AHRS_NavEKF &get_ahrs(void) { return frontend._ahrs; }
 
     // get ADDR parameter value
     uint8_t get_address(void) const { return frontend._address; }