flutter: Remove legacy regret code

src/ui/flutter_app/lib/l10n/intl_en.arb

@@ -284,10 +284,6 @@
   "@youLose": {
     "description": "You Lose!"
   },
-  "regret": "Undo",
-  "@regret": {
-    "description": "Undo"
-  },
   "analyze": "Analyze",
   "@analyze": {
     "description": "Analyze"

src/ui/flutter_app/lib/l10n/intl_zh.arb

@@ -71,7 +71,6 @@
   "youWin": "恭喜你赢了",
   "challengeHarderLevel": "后续提升难度吗？\n提升后的难度等级将为",
   "youLose": "你输了",
-  "regret": "悔棋",
   "analyze": "分析",
   "playerName": "棋手姓名",
   "about": "关于",

src/ui/flutter_app/lib/mill/game.dart

@@ -139,47 +139,6 @@ class Game {
     return true;
   }
 
-  bool regret({moves = 2}) {
-    //
-    // Can regret only our turn
-    // TODO
-    if (_position.side != PieceColor.black) {
-      //Audios.playTone(Audios.invalidSoundId);
-      return false;
-    }
-
-    var regretted = false;
-
-    /// Regret 2 step
-
-    for (var i = 0; i < moves; i++) {
-      //
-      if (!_position.regret()) break;
-
-      final lastMove = _position.lastMove;
-
-      if (lastMove != null) {
-        //
-        _blurIndex = lastMove.from ?? invalidIndex;
-        _focusIndex = lastMove.to ?? invalidIndex;
-        //
-      } else {
-        //
-        _blurIndex = _focusIndex = invalidIndex;
-      }
-
-      regretted = true;
-    }
-
-    if (regretted) {
-      //Audios.playTone(Audios.regretSoundId);
-      return true;
-    }
-
-    //Audios.playTone(Audios.invalidSoundId);
-    return false;
-  }
-
   printStat() {
     double whiteWinRate = 0;
     double blackWinRate = 0;

src/ui/flutter_app/lib/mill/position.dart

@@ -1062,45 +1062,6 @@ class Position {
     Game.instance.setWhoIsAi(engineTypeBackup);
   }
 
-  bool regret() {
-    // TODO
-    final lastMove = recorder!.removeLast();
-    if (lastMove == null) return false;
-
-    _grid[lastMove.from] = _grid[lastMove.to];
-    _grid[lastMove.to] = lastMove.removed;
-    board[lastMove.from] = board[lastMove.to];
-    board[lastMove.to] = lastMove.removed;
-
-    changeSideToMove();
-
-    final counterMarks = GameRecorder.fromCounterMarks(lastMove.counterMarks);
-    recorder!.halfMove = counterMarks.halfMove;
-    recorder!.fullMove = counterMarks.fullMove;
-
-    if (lastMove.removed != Piece.noPiece) {
-      //
-      // Find last remove position (or opening), NativeEngine need
-      final tempPosition = Position.clone(this);
-
-      final moves = recorder!.reverseMovesToPrevRemove();
-      moves.forEach((move) {
-        //
-        tempPosition._grid[move.from] = tempPosition._grid[move.to];
-        tempPosition._grid[move.to] = move.removed;
-
-        tempPosition._sideToMove =
-            PieceColor.opponent(tempPosition._sideToMove);
-      });
-
-      recorder!.lastPositionWithRemove = tempPosition.fen();
-    }
-
-    result = GameResult.pending;
-
-    return true;
-  }
-
   String movesSinceLastRemove() {
     int? i = 0;
     String moves = "";