Service Worker:Layouttests:Remove wrong done() call from serviceworkerobject-scripturl.html

1. Due to misplace "t.done()", get the undefined registration,and the assert_equals will always be not excuted.

R=nhiroki@chromium.org, dominicc@chromium.org, yhirano@chromium.org
BUG=414599

Review URL: https://codereview.chromium.org/579693002

git-svn-id: svn://svn.chromium.org/blink/trunk@182215 bbb929c8-8fbe-4397-9dbb-9b2b20218538