Remove fourth argument to createNodeIterator/createTreeWalker

http://dom.spec.whatwg.org/#dom-document-createnodeiterator
http://dom.spec.whatwg.org/#dom-document-createtreewalker

As shown by the test cases, the extra argument is ignored, so it does
not need to be in the IDL in order to be compatible with legacy code.

BUG=325922

Review URL: https://codereview.chromium.org/106423002

git-svn-id: svn://svn.chromium.org/blink/trunk@163271 bbb929c8-8fbe-4397-9dbb-9b2b20218538