Don't need to init board[] with NO_PIECE

Now that NO_PIECE == 0 the common memset() will
do the work.

No functional change.

src/position.cpp

@@ -1347,9 +1347,6 @@ void Position::clear() {
   for (int i = 0; i < 8; i++)
       for (int j = 0; j < 16; j++)
           pieceList[0][i][j] = pieceList[1][i][j] = SQ_NONE;
-
-  for (Square sq = SQ_A1; sq <= SQ_H8; sq++)
-      board[sq] = NO_PIECE;
 }