Remove some dead code from rendering/ folder

Remove some dead code from rendering/ folder. Several methods were defined but
never used.

R=esprehn@chromium.org, pdr@chromium.org

Review URL: https://codereview.chromium.org/241713002

git-svn-id: svn://svn.chromium.org/blink/trunk@171899 bbb929c8-8fbe-4397-9dbb-9b2b20218538