Remove android_... store_barriers and 64-bit atomics.

These are no longer used, and we want to strongly discourage future use.
Keep the 32-bit variants while there are still uses.  All users should move
to C11 or C++11 atomics.

(Resolved conflicts in atomic-...64.h with uniprocessor support
removal as in AOSP.)

Bug:16880454

Change-Id: I122b541cfd29ef4a6c932647f85d0d6a9d802061
(cherry picked from commit 9959ed95)