Remove unnecessary comments left from eariler code cleanup

TBR=wangxianzhu@chromium.org
NOTRY=true

Review URL: https://codereview.chromium.org/601413002

git-svn-id: svn://svn.chromium.org/blink/trunk@182714 bbb929c8-8fbe-4397-9dbb-9b2b20218538