Migrate away from symlinks to ease builds on Windows

[supersat]

Currently android/app/prebuilt/armeabi-v7a/lib*.so are symlinked to their corresponding files built in libosmocore. On systems where WSL is used to build libosmocore/osmocom-bb and Android Studio is used to build the app, this breaks because WSL symlinks are not the same as regular NTFS symlinks. In many cases, NTFS symlinks also require administrator permissions to create. It should be relatively easy to just copy these libraries over as part of the Android build process.