Remove TestExpectations entry for xmlhttprequest-timeout-worker-simple.html

It's no longer flaky.
http://test-results.appspot.com/dashboards/flakiness_dashboard.html#tests=http%2Ftests%2Fxmlhttprequest%2Ftimeout%2Fxmlhttprequest-timeout-worker-simple.html

R=hiroshige
BUG=311467

Review URL: https://codereview.chromium.org/578413004

git-svn-id: svn://svn.chromium.org/blink/trunk@182302 bbb929c8-8fbe-4397-9dbb-9b2b20218538