Don't include QtWebView components in WinRT/Winphone installers

QtWebView not supported by WinRT/Winphone so remove it from offline
installers.

Task-number: QTBUG-42555
Change-Id: Id261d5ba5f6e00ec5952a4ef9c1d68b029131ada
Reviewed-by: Antti Kokko <antti.kokko@digia.com>