Remove piece lists

This patch removes the incrementally updated piece lists from the Position object.

This has been tried before but always failed. My reasons for trying again are:

* 32-bit systems (including phones) are now much less important than they were some years ago (and are absent from fishtest);
* NNUE may have made SF less finely tuned to the order in which moves were generated.

STC:
LLR: 2.94 (-2.94,2.94) {-1.25,0.25}
Total: 55272 W: 5260 L: 5216 D: 44796
Ptnml(0-2): 208, 4147, 18898, 4159, 224
https://tests.stockfishchess.org/tests/view/5fc2986a42a050a89f02c926

LTC:
LLR: 2.96 (-2.94,2.94) {-0.75,0.25}
Total: 16600 W: 673 L: 608 D: 15319
Ptnml(0-2): 14, 533, 7138, 604, 11
https://tests.stockfishchess.org/tests/view/5fc2f98342a050a89f02c95c

closes https://github.com/official-stockfish/Stockfish/pull/3247

Bench: 3940967

src/position.cpp

@@ -197,7 +197,6 @@ Position& Position::set(const string& fenStr, bool isChess960, StateInfo* si, Th
 
   std::memset(this, 0, sizeof(Position));
   std::memset(si, 0, sizeof(StateInfo));
-  std::fill_n(&pieceList[0][0], sizeof(pieceList) / sizeof(Square), SQ_NONE);
   st = si;
 
   ss >> std::noskipws;
@@ -1327,16 +1326,10 @@ bool Position::pos_is_ok() const {
       assert(0 && "pos_is_ok: State");
 
   for (Piece pc : Pieces)
-  {
       if (   pieceCount[pc] != popcount(pieces(color_of(pc), type_of(pc)))
           || pieceCount[pc] != std::count(board, board + SQUARE_NB, pc))
           assert(0 && "pos_is_ok: Pieces");
 
-      for (int i = 0; i < pieceCount[pc]; ++i)
-          if (board[pieceList[pc][i]] != pc || index[pieceList[pc][i]] != i)
-              assert(0 && "pos_is_ok: Index");
-  }
-
   for (Color c : { WHITE, BLACK })
       for (CastlingRights cr : {c & KING_SIDE, c & QUEEN_SIDE})
       {