Heart Rate Monitor example for the BLE API using nRF51822 native mode drivers

Dependencies:   BLE_API mbed nRF51822 X_NUCLEO_IDB0XA1

remove BLE_HeartRate.lib file

in rev 50:477004d54431, a BLE_HeartRate.lib file has been committed which points to 'itself'. remove it

Heart Rate Monitor example for the BLE API using nRF51822 native mode drivers