Hide AssetInputStream.getAssetInt.

It returns a pointer to a private data structure, so there's
no sensible use for it. Also, the emergence of 64 bit processors
means that the return value isn't wide enough to represent
values in the native heap.

(cherry picked from commit f8f09a15)

Change-Id: I9c9b5bae6db8638e65dda60f924aa3dddd06813a