DevTools: more css/domModel accessors removed, activeTargetChanged event removed.

R=sergeyv@chromium.org

Review URL: https://codereview.chromium.org/227673002

git-svn-id: svn://svn.chromium.org/blink/trunk@170968 bbb929c8-8fbe-4397-9dbb-9b2b20218538