windows: do not replace sys.__stdout__

windows: do not replace sys.__stdout__

Now we don't use sys.__stdout__ except for getting its fileno(), so we no
longer have to wrap it by winstdout.

This helps adding pycompat.stdin/out/err.

--- a/mercurial/windows.py	Mon Nov 21 15:38:56 2016 +0530
+++ b/mercurial/windows.py	Thu Oct 20 23:27:09 2016 +0900
@@ -171,7 +171,7 @@
             self.close()
             raise IOError(errno.EPIPE, 'Broken pipe')
 
-sys.__stdout__ = sys.stdout = winstdout(sys.stdout)
+sys.stdout = winstdout(sys.stdout)
 
 def _is_win_9x():
     '''return true if run on windows 95, 98 or me.'''