`isWinVistaOrHigher` in `DownloadsCommon` is no longer used, and the relevant code will be deleted through this commit. Differential Revision: https://phabricator.services.mozilla.com/D171314
`isWinVistaOrHigher` in `DownloadsCommon` is no longer used, and the relevant code will be deleted through this commit. Differential Revision: https://phabricator.services.mozilla.com/D171314