Retire UCI_Chess960 option

We don't need that !

We can infere from starting fen string if we are in
a Chess960 game or not. And note that this is a per-position
property, not an application wide one.

A nice trick is to use a custom manipulator (that is an
enum actually) to keep using the handy operator<<() on the
move when sending to std::cout, yes, I have indulged a
bit here ;-)

Signed-off-by: Marco Costalba <mcostalba@gmail.com>

src/ucioption.cpp

@@ -131,7 +131,6 @@ namespace {
     o["Emergency Base Time"] = Option(200, 0, 60000);
     o["Emergency Move Time"] = Option(70, 0, 5000);
     o["Minimum Thinking Time"] = Option(20, 0, 5000);
-    o["UCI_Chess960"] = Option(false);
     o["UCI_AnalyseMode"] = Option(false);
 
     // Any option should know its name so to be easily printed