Remove Windows L&F backup icons

Windows L&F has a set of icons in:
src/share/classes/com/sun/java/swing/plaf/windows/icons

Most of these icons are simply backups for when the L&F fails to load the correct icons from the native system. However, I can no longer think of any case when this would happen. As such, these should be removed. Any code that references them directly should be changed to pull the proper images from the OS.