Remove unused cruft from GraphicsLayer

This CL deletes a bunch of state and code from GraphicsLayer that's not used.

R=jamesr@chromium.org

Review URL: https://codereview.chromium.org/335453002

git-svn-id: svn://svn.chromium.org/blink/trunk@176005 bbb929c8-8fbe-4397-9dbb-9b2b20218538