chore: remove useless code

__HAL_RCC_GET_RTC_SOURCE was added since STM32Cube HAL V1.2.5

Signed-off-by: Frederic Pillon <frederic.pillon@st.com>

Author: fpistm

src/rtc.h

@@ -155,18 +155,6 @@ typedef void(*voidCallbackPtr)(void *);
 #define IS_RTC_HOUR12(HOUR)      IS_RTC_HOUR24(HOUR)
 #endif /* !STM32F1xx && !IS_RTC_WEEKDAY */
 
-/* __HAL_RCC_GET_RTC_SOURCE is not defined for F2*/
-/*
-#ifndef __HAL_RCC_GET_RTC_SOURCE
-static uint32_t RTC_getSource(void) {
-  RCC_PeriphCLKInitTypeDef  *PeriphClkInit;
-  HAL_RCCEx_GetPeriphCLKConfig(PeriphClkInit);
-  return PeriphClkInit->RTCClockSelection;
-}
-#define __HAL_RCC_GET_RTC_SOURCE()  RTC_getSource()
-#endif
-*/
-
 /* Exported macro ------------------------------------------------------------*/
 /* Exported functions ------------------------------------------------------- */
 void RTC_SetClockSource(sourceClock_t source);