install libs built Android-style into libs/$(APP_ABI)/ instead of assets/

This means that Android handles the rest for us, including bundling and
unpacking them from the APK, setting the LD_LIBRARY_PATH, etc.

refs #1548
load native libs via standard path (libgpg-error, libassuan, libgpgme)

Now that the core libs are included in the standard Android way, we can
load the libs in the standard Android way.

#1548
remove manual entry for libs/, its included automatically