ServiceWorker: Remove unnecessary NeedsRebaseline for fetch-event.html

BUG=388375,401381
TBR=nhiroki@chromium.org
NOTRY=true

Review URL: https://codereview.chromium.org/642933008

git-svn-id: svn://svn.chromium.org/blink/trunk@183640 bbb929c8-8fbe-4397-9dbb-9b2b20218538