Update outdated comments

closes https://github.com/official-stockfish/Stockfish/pull/5158

No functional change

src/position.cpp

@@ -744,7 +744,6 @@ void Position::do_move(Move m, StateInfo& newSt, bool givesCheck) {
         // Update board and piece lists
         remove_piece(capsq);
 
-        // Update material hash key and prefetch access to materialTable
         k ^= Zobrist::psq[captured][capsq];
         st->materialKey ^= Zobrist::psq[captured][pieceCount[captured]];