Crash trying to render a SVGFEDistantLightElement

Override rendererIsNeeded() in SVGFELightElement to return false so that we
don't attempt to render such elements. This is a regression from r155426.

TBR=pdr@chromium.org
BUG=267824

Review URL: https://codereview.chromium.org/22043002

git-svn-id: svn://svn.chromium.org/blink/trunk@155469 bbb929c8-8fbe-4397-9dbb-9b2b20218538