remove the redundant #define

Those #define never used.

Author: TsungtaWu

targets/TARGET_NORDIC/TARGET_NRF5/TARGET_MCU_NRF52832/TARGET_DELTA_DFBM_NQ620/mbed_overrides.c

@@ -13,9 +13,7 @@
  * See the License for the specific language governing permissions and
  * limitations under the License.
  */
-	#define MBED_CONF_NORDIC_NRF_LF_CLOCK_SRC		(NRF_LF_SRC_RC)
-	#define MBED_CONF_NORDIC_NRF_LF_CLOCK_CALIB_TIMER_INTERVAL	16
-	#define MBED_CONF_NORDIC_NRF_LF_CLOCK_CALIB_MODE_CONFIG	1
+
 void mbed_sdk_init()
 {
 	printf("", __TIME__, __DATE__);