Revert "Revert "Revert "Revert "Remove incorrect android_atomic_...64 use.""""

After fixing b/16874785.

This reverts commit f010a05c.

Original comment, which actually describes the effect of this:

Change the mExtras field in Binder.h to be a stdatomic.h atomic
value, and replace references to it with proper stdatomic.h calls.
This removes one of a small number of remaining 64 bit
android_atomic references.  It also replaces the erroneously
non-atomic read accesses to mExtras.

It would be better if this used the C++11 <atomic> facility,
but we don't quite have that yet.

Fixes

Bug:16513433

Change-Id: I1645ca5d6f60595bf5d388913665ce4b8780b26d
(cherry picked from commit 3effabab)