Remove deprecated markersForNode(Node* node)

DocumentMarkerController::markersForNode(Node* node) has been marked as
deprecated in favor of markersFor(Node*, MarkerTypes = AllMarkers()).

WebKit changeset: http://trac.webkit.org/changeset/155095

BUG=

Review URL: https://chromiumcodereview.appspot.com/23903015

git-svn-id: svn://svn.chromium.org/blink/trunk@157294 bbb929c8-8fbe-4397-9dbb-9b2b20218538