Cleaning out unneeded WebGL DebugRenderInfo finch experiment plumbing

Chrome side CL: https://codereview.chromium.org/142493003/

BUG=335373

Review URL: https://codereview.chromium.org/141863002

git-svn-id: svn://svn.chromium.org/blink/trunk@166337 bbb929c8-8fbe-4397-9dbb-9b2b20218538