Remove leftover code from InspectorController.

'PostWorkerNotificationToFrontendTask' was removed in r108965.
(http://trac.webkit.org/changeset/108965)

BUG=none.

Review URL: https://codereview.chromium.org/105633008

git-svn-id: svn://svn.chromium.org/blink/trunk@164157 bbb929c8-8fbe-4397-9dbb-9b2b20218538