Make sure LPTICKER symbols are not used for builds without it for Nordic

targets/TARGET_NORDIC/TARGET_NRF5x/TARGET_NRF51/flash_api.c

@@ -36,7 +36,7 @@
  *
  */
 
-#if DEVICE_FLASH
+#if (defined(DEVICE_FLASH) && defined(DEVICE_LPTICKER))
 
 #include "hal/flash_api.h"
 #include "hal/lp_ticker_api.h"

targets/TARGET_NORDIC/TARGET_NRF5x/TARGET_NRF51/trng_api.c

@@ -36,7 +36,7 @@
  *
  */
 
-#if defined(DEVICE_TRNG)
+#if (defined(DEVICE_TRNG) && defined(DEVICE_LPTICKER))
 
 #include "hal/trng_api.h"
 #include "hal/lp_ticker_api.h"

targets/targets.json

@@ -3511,8 +3511,7 @@
             "TARGET_MCU_NRF51822",
             "CMSIS_VECTAB_VIRTUAL",
             "CMSIS_VECTAB_VIRTUAL_HEADER_FILE=\"cmsis_nvic.h\"",
-            "NO_SYSTICK",
-            "MBED_TICKLESS"
+            "NO_SYSTICK"
         ],
         "MERGE_BOOTLOADER": false,
         "extra_labels": [
@@ -3598,7 +3597,6 @@
             "I2C_ASYNCH",
             "INTERRUPTIN",
             "ITM",
-            "LOWPOWERTIMER",
             "PORTIN",
             "PORTINOUT",
             "PORTOUT",