Remove empty methods from WebScriptController.

Now that Chromium was updated to not call these empty methods, we can
remove them from Blink.

Chromium change is:
https://src.chromium.org/viewvc/chrome?view=rev&revision=251716

BUG=None
TEST=None
R=abarth@chromium.org

Review URL: https://codereview.chromium.org/171723003

git-svn-id: svn://svn.chromium.org/blink/trunk@167496 bbb929c8-8fbe-4397-9dbb-9b2b20218538