Remove support for <animateColor>.

Makes SVGAnimateColorElement an unknown DOM interface, but preserves HTML5 parsing rules (e.g ANIMATECOLOR -> animateColor).

BUG=332839

Review URL: https://codereview.chromium.org/137443006

git-svn-id: svn://svn.chromium.org/blink/trunk@165071 bbb929c8-8fbe-4397-9dbb-9b2b20218538