Remove fflush call from tui_refresh_cmd_win

tui_refresh_cmd_win calls fflush, but there's a comment explaining
that the reason for the call is unknown.  This patch removes the call.
I don't think it can be useful, since gdb doesn't generally use stdout
in this way -- only through ui_file.

gdb/tui/tui-command.c

@@ -64,9 +64,4 @@ tui_refresh_cmd_win (void)
   WINDOW *w = TUI_CMD_WIN->handle.get ();
 
   tui_wrefresh (w);
-
-  /* FIXME: It's not clear why this is here.
-     It was present in the original tui_puts code and is kept in order to
-     not introduce some subtle breakage.  */
-  fflush (stdout);
 }