Retire pieces_of_color_and_type()

It is used mainly in a bunch of inline oneliners
just below its definition. So substitute it with
the explicit definition and avoid information hiding.

No functional change.

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

src/movegen.cpp

@@ -832,7 +832,7 @@ namespace {
   MoveStack* generate_piece_checks(const Position& pos, MoveStack* mlist, Color us,
                                    Bitboard dc, Square ksq) {
 
-    Bitboard target = pos.pieces_of_color_and_type(us, Piece);
+    Bitboard target = pos.pieces_of_color(us) & pos.pieces_of_type(Piece);
 
     // Discovered checks
     Bitboard b = target & dc;