Replace Doxygen link in BatteryService.md

Transclude .h file instead of class because the class page no longer exists.

Author: Amanda Butler

docs/api/bluetooth/BatteryService.md

@@ -8,7 +8,7 @@ The BatteryService class implements the Bluetooth Battery Service as defined by
 
 ### BatteryService class reference
 
-[![View code](https://www.mbed.com/embed/?type=library)](https://os.mbed.com/docs/development/mbed-os-api-doxy/class_battery_service.html)
+[![View code](https://www.mbed.com/embed/?type=library)](https://os.mbed.com/docs/mbed-os/development/mbed-os-api-doxy/_battery_service_8h_source.html)
 
 ### BatteryService example