[Android] Fix generate_app_packaging_tool to only copy what it needs

Previously it was copying the entire xwalk_core_library which drags
uneeded stuff and therefore cary them in the final application APK.
This fixes the bug of DeviceCapabilities APIs not working because
it was loading files in the raw/ directory which should not have
been there in the first place.

BUG=XWALK-2184