NRFCordioHCIDriver: remove idle_hook

In PR #8876 when we added Cordio support for nRF52* targets,
we attempted to use an RTOS idle hook to workaround sleep
latency issues. However, the condition to bypass sleeps
never gets satisfied, and BLE nRF52* targets have generally
worked fine over the past year.

This commit removes the hook to avoid dependency on RTOS,
enabling BLE on bare metal.

Author: LDong-Arm

features/FEATURE_BLE/targets/TARGET_NORDIC/TARGET_NORDIC_CORDIO/TARGET_NRF5x/NRFCordioHCIDriver.cpp

@@ -21,7 +21,6 @@
 
 // mbed Includes
 #include "mbed_assert.h"
-#include "rtos/source/rtos_idle.h"
 #include "platform/mbed_power_mgmt.h"
 #include "mbed_critical.h"
 
@@ -183,30 +182,6 @@ const LlRtCfg_t NRFCordioHCIDriver::_ll_cfg = {
 
 extern "C" void TIMER0_IRQHandler(void);
 
-static void idle_hook(void)
-{
-	wsfTimerTicks_t nextExpiration;
-	bool_t          timerRunning;
-
-	nextExpiration = WsfTimerNextExpiration(&timerRunning);
-	if(timerRunning && nextExpiration > 0)
-	{
-		// Make sure we hae enough time to go to sleep
-		if( nextExpiration < 1 /* 10 ms per tick which is long enough to got to sleep */ )
-		{
-			// Bail
-			return;
-		}
-	}
-
-    // critical section to complete sleep with locked deepsleep
-    core_util_critical_section_enter();
-    sleep_manager_lock_deep_sleep();
-    sleep();
-    sleep_manager_unlock_deep_sleep();
-    core_util_critical_section_exit();
-}
-
 NRFCordioHCIDriver::NRFCordioHCIDriver(CordioHCITransportDriver& transport_driver) : cordio::CordioHCIDriver(transport_driver), _is_init(false), _stack_buffer(NULL)
 {
     _stack_buffer = (uint8_t*)malloc(CORDIO_LL_MEMORY_FOOTPRINT);
@@ -234,9 +209,6 @@ NRFCordioHCIDriver::~NRFCordioHCIDriver()
     free(_stack_buffer);
     _stack_buffer = NULL;
 
-    // Restore RTOS idle thread
-	rtos_attach_idle_hook(NULL);
-
     MBED_ASSERT(_stack_buffer == NULL);
 }
 
@@ -281,9 +253,6 @@ void NRFCordioHCIDriver::do_initialize()
         .freeMemAvail = CORDIO_LL_MEMORY_FOOTPRINT
     };
 
-    // Override RTOS idle thread
-    rtos_attach_idle_hook(idle_hook);
-
     /* switch to more accurate 16 MHz crystal oscillator (system starts up using 16MHz RC oscillator) */
     NRF_CLOCK->EVENTS_HFCLKSTARTED = 0;
     NRF_CLOCK->TASKS_HFCLKSTART    = 1;