Remove unused directories

Because of how we update the libvpx checkout, some removed directories
are not managed.

Compared to an upstream checkout and removed directories which no
longer exist upstream.



git-svn-id: http://src.chromium.org/svn/trunk/deps/third_party/libvpx@291832 4ff67af0-8c30-449e-8e8b-ad334ec8d88c