Remove BindingSecurity::shouldAllowAccessToDOMWindow.

We're not using this anywhere. If we end up needing it, we can always
bring it back via the magic of 'git revert'.

Review URL: https://chromiumcodereview.appspot.com/22800003

git-svn-id: svn://svn.chromium.org/blink/trunk@155930 bbb929c8-8fbe-4397-9dbb-9b2b20218538