Unify the two copies of move.h

This patch basically deletes webrtc/base/move.h (which is the more
outdated copy) and moves webrtc/system_wrappers/source/move.h to take
its place.

R=andrew@webrtc.org

Review URL: https://webrtc-codereview.appspot.com/35549004

git-svn-id: http://webrtc.googlecode.com/svn/trunk@7963 4adac7df-926f-26a2-2b94-8c16560cd09d