remove flush hook cruft that was never used from stdio

there is no need/use for a flush hook. the write function serves this
purpose already. i originally created the hook for implementing mem
streams based on a mistaken reading of posix, and later realized it
wasn't useful but never removed it until now.

src/stdio/freopen.c

@@ -32,7 +32,6 @@ FILE *freopen(const char *filename, const char *mode, FILE *f)
 	f->write = f2->write;
 	f->seek = f2->seek;
 	f->close = f2->close;
-	f->flush = f2->flush;
 
 	fclose(f2);
 	return f;