Get rid of 'hasFrontend()' in InspectorController and WorkerInspectorController.

This CL remove 'hasFrontend()' from InspectorController and WorkerInspectorController
as it's never called.

BUG=none.

Review URL: https://codereview.chromium.org/100683003

git-svn-id: svn://svn.chromium.org/blink/trunk@163109 bbb929c8-8fbe-4397-9dbb-9b2b20218538