Remove Unused measure DocumentCreateAttributeNS

Intent to Remove:
    https://groups.google.com/a/chromium.org/forum/#!topic/blink-dev/8p-gwWL4ypc

BUG=341830

Review URL: https://codereview.chromium.org/158593003

git-svn-id: svn://svn.chromium.org/blink/trunk@166794 bbb929c8-8fbe-4397-9dbb-9b2b20218538