AP_InertialSensor: removed timer callback for MPU6000

Thanks to Lucas for pointing out this is not needed

libraries/AP_InertialSensor/AP_InertialSensor_MPU6000.cpp

@@ -280,6 +280,9 @@ AP_InertialSensor_Backend *AP_InertialSensor_MPU6000::probe(AP_InertialSensor &i
                                                             AP_HAL::OwnPtr<AP_HAL::SPIDevice> dev,
                                                             enum Rotation rotation)
 {
+    if (!dev) {
+        return nullptr;
+    }
     AP_InertialSensor_MPU6000 *sensor;
 
     dev->set_read_flag(0x80);
@@ -409,10 +412,7 @@ void AP_InertialSensor_MPU6000::start()
     set_accel_orientation(_accel_instance, _rotation);
     
     // start the timer process to read samples
-    if (_dev->register_periodic_callback(1000, FUNCTOR_BIND_MEMBER(&AP_InertialSensor_MPU6000::_poll_data, bool)) == nullptr) {
-        // cope with AuxiliaryBus which does not support register_periodic_callback yet
-        hal.scheduler->register_timer_process(FUNCTOR_BIND_MEMBER(&AP_InertialSensor_MPU6000::_poll_data_timer, void));
-    }
+    _dev->register_periodic_callback(1000, FUNCTOR_BIND_MEMBER(&AP_InertialSensor_MPU6000::_poll_data, bool));
 }
 
 /*
@@ -469,18 +469,6 @@ bool AP_InertialSensor_MPU6000::_poll_data()
     return true;
 }
 
-/*
-  varient of _poll_data for systems where register_periodic_callback
-  fails. We need to handle the semaphore ourselves.
- */
-void AP_InertialSensor_MPU6000::_poll_data_timer()
-{
-    if (_dev->get_semaphore()->take_nonblocking()) {
-        _poll_data();
-        _dev->get_semaphore()->give();
-    }
-}
-
 void AP_InertialSensor_MPU6000::_accumulate(uint8_t *samples, uint8_t n_samples)
 {
     for (uint8_t i = 0; i < n_samples; i++) {

libraries/AP_InertialSensor/AP_InertialSensor_MPU6000.h

@@ -82,7 +82,6 @@ private:
 
     /* Poll for new data (non-blocking) */
     bool _poll_data();
-    void _poll_data_timer();
 
     /* Read and write functions taking the differences between buses into
      * account */