Remove WindowController.openExternal
Remove WindowController.openExternal

The method existed for two obsolete reasons:

① to work around a bug in old IE that we no longer care about, and
② to scrub the referrer, which can instead be done with the
  Referrer-Policy header.

Therefore it has no place in the bundle, and should be removed.

Users should replace this:

    WindowController.openExternal( url )

With this:

    open( url, '_blank', 'noopener' );

And ensure that you have an appropriate Referrer Policy.

fastmail/overture