Retire Polyglot Book management

Book handling belongs to GUI, we kept this code
for historical reasons, but nowdays there is
really no need of this old, (mostly) unused
and especially incorrect designed functionality.

It is up to the GUI to choose the book (far easier for
the user) and to select the book parameters. In no
place, including fishtest, TCEC, rating lists, etc.
the "own book" is used, moreover currently SF is
released without any book and even if in the future we
bundle a book in the release package, it will be the GUI
that will take care of it.

This corrects a wrong design decision that Galurung
and later Stockfish inherited from what was common
practice many yeas ago.

No functional change.

src/types.h

@@ -136,7 +136,7 @@ enum CastlingSide {
   KING_SIDE, QUEEN_SIDE, CASTLING_SIDE_NB = 2
 };
 
-enum CastlingRight {  // Defined as in PolyGlot book hash key
+enum CastlingRight {
   NO_CASTLING,
   WHITE_OO,
   WHITE_OOO   = WHITE_OO << 1,