Remove all traces of compositing reasons from cc

This information is now coming in via the debug info. Lots of stuff may
disappear now.

BUG=None
R=jamesr@chromium.org

Review URL: https://codereview.chromium.org/128263006

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@244190 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 244190