Revert "[WIN32] changed: set background mode when minimized. prevents sc...

...reen saver to kick in."

This reverts commit 872d58c73dcb40f5f7bf71a2d1e4509e676f07e0.

fixes ResetScreenSaver for platforms not using background flag. also fix high cpu load when minimized https://github.com/xbmc/xbmc/pull/4617