Retire xmlhttprequest/workers/close.html test expectation.

Test is no longer reported as timing out on Windows bots.

R=tyoshino@chromium.org
BUG=409535
NOTRY=true

Review URL: https://codereview.chromium.org/711013002

git-svn-id: svn://svn.chromium.org/blink/trunk@185042 bbb929c8-8fbe-4397-9dbb-9b2b20218538