Remove 64-bit android_atomic uses from StateQueue.

Use stdatomic.h instead.  We're trying to remove android_atomic use
wherever possible.  The 64-bit uses seem easiest to remove first.
This cleans up the code, though not as much as C++ <atomic> would,
if it worked everywhere.

Change-Id: I3c29bdbd5915cb9d47118834a3a742fe296cf87f