Move rtc::AtomicOps to webrtc/base/atomicops.h.

Removes FixedSizeLockFreeQueue which isn't used anymore. This enabled
moving rtc::AtomicOps to webrtc/base/atomicops.h where they should be.

BUG=4330
R=tommi@webrtc.org

Review URL: https://webrtc-codereview.appspot.com/51789004

Cr-Commit-Position: refs/heads/master@{#9120}
9 files changed