Fix MTB_MTS_XDOT build breakage

Author: SenRamakri

targets/TARGET_STM/TARGET_STM32L1/TARGET_MTB_MTS_XDOT/device/system_clock.c

@@ -249,12 +249,4 @@ uint8_t SetSysClock_PLL_HSI(void)
     return 1; // OK
 }
 
-/******************************************************************************/
-/*            Hard Fault Handler                                              */
-/******************************************************************************/
-void HardFault_Handler(void)
-{
-    debug("Hard Fault\n");
-    NVIC_SystemReset();
-}