[Patch] Don't include <fstream> in include/ext/stdio_sync_filebuf.h

[Pétur Runólfsson]

Paolo Carlini wrote:
> 
> > Hi,
> >
> > working on 12077 I noticed this include, which seems redundant.
> > Indeed, I removed it and successfully regtested.
> 
> Forget about this, sorry. However, we could probably include much less...

Yes, only <cstdio> (for FILE, getc, etc.), <cwchar> (for getwc etc.)
and <streambuf> should be needed.

Petur