Remove temporarily kept WebKit API when renaming command line switch

BUG=367082
TBR=eae,dpranke

Review URL: https://codereview.chromium.org/264603003

git-svn-id: svn://svn.chromium.org/blink/trunk@173326 bbb929c8-8fbe-4397-9dbb-9b2b20218538