RTOS: use default boot-stack-size for NRF52* as SoftDevice is no longer used

Previously we overrode NRF targets to have a larger stack
due to memory required by SoftDevice. Having deprecated SoftDevice
in favour of Cordio for BLE (#12674), such requirement does not
apply anymore.

Author: LDong-Arm

TESTS/mbed_hal/stack_size_unification/main.cpp

@@ -31,10 +31,7 @@ extern osThreadAttr_t _main_thread_attr;
 #endif
 extern uint32_t mbed_stack_isr_size;
 
-/* Exception for Nordic boards - BLE requires 2KB ISR stack. */
-#if defined(TARGET_NRF5x)
-#define EXPECTED_ISR_STACK_SIZE                  (2048)
-#elif !defined(MBED_CONF_RTOS_PRESENT)
+#if !defined(MBED_CONF_RTOS_PRESENT)
 #define EXPECTED_ISR_STACK_SIZE                  (4096)
 #else
 #define EXPECTED_ISR_STACK_SIZE                  (1024)

rtos/source/TARGET_CORTEX/mbed_lib.json

@@ -79,12 +79,6 @@
         "MCU_NRF51": {
             "target.boot-stack-size": "0x800"
         },
-        "MCU_NRF52840": {
-            "target.boot-stack-size": "0x800"
-        },
-        "MCU_NRF52832": {
-            "target.boot-stack-size": "0x800"
-        },
         "MCU_NRF51_UNIFIED": {
             "target.boot-stack-size": "0x800"
         },