Unload oat files

Unregister and delete oat file when we call DexFile.closeDexFile if
all of the dex files are no longer in use. We store the oat file as
the first element of the dex files array (cookie).

Added a test that reads the proc maps to ensure there are no
unload-ex maps. Also some clean up.

Bug: 22720414

Change-Id: I52ab84562d1045e94b9a37aafe57609a14f188f7
9 files changed