Remove more dead code from accessibility/ folder

Remove more dead code from accessibility/ folder. Several functions were
defined but never used.

R=dmazzoni@chromium.org

Review URL: https://codereview.chromium.org/243083002

git-svn-id: svn://svn.chromium.org/blink/trunk@172018 bbb929c8-8fbe-4397-9dbb-9b2b20218538