Remove unnecessary crash expectation for xmlviewer/extensions-api.html

TBR=jsbell@chromium.org
BUG=264501

Review URL: https://codereview.chromium.org/35753004

git-svn-id: svn://svn.chromium.org/blink/trunk@160264 bbb929c8-8fbe-4397-9dbb-9b2b20218538