remove unused code

src/ui/flutter_app/lib/screens/game_settings/game_settings_page.dart

@@ -22,7 +22,6 @@ import 'dart:io';
 import 'package:flutter/material.dart';
 import 'package:hive_flutter/hive_flutter.dart' show Box;
 import 'package:sanmill/generated/l10n.dart';
-import 'package:sanmill/models/display.dart';
 import 'package:sanmill/models/preferences.dart';
 import 'package:sanmill/models/temporary.dart';
 import 'package:sanmill/screens/env_page.dart';
@@ -111,20 +110,6 @@ class GameSettingsPage extends StatelessWidget {
     debugPrint("$_tag isAutoRestart: $value");
   }
 
-  void _setIsAutoChangeFirstMove(Preferences _preferences, bool value) {
-    LocalDatabaseService.preferences =
-        _preferences.copyWith(isAutoChangeFirstMove: value);
-
-    debugPrint("$_tag isAutoChangeFirstMove: $value");
-  }
-
-  void _setResignIfMostLose(Preferences _preferences, bool value) {
-    LocalDatabaseService.preferences =
-        _preferences.copyWith(resignIfMostLose: value);
-
-    debugPrint("$_tag resignIfMostLose: $value");
-  }
-
   void _setShufflingEnabled(Preferences _preferences, bool value) {
     LocalDatabaseService.preferences =
         _preferences.copyWith(shufflingEnabled: value);
@@ -132,20 +117,6 @@ class GameSettingsPage extends StatelessWidget {
     debugPrint("$_tag shufflingEnabled: $value");
   }
 
-  void _setLearnEndgame(Preferences _preferences, bool value) {
-    LocalDatabaseService.preferences =
-        _preferences.copyWith(learnEndgame: value);
-
-    debugPrint("$_tag learnEndgame: $value");
-  }
-
-  void _setOpeningBook(Preferences _preferences, bool value) {
-    LocalDatabaseService.preferences =
-        _preferences.copyWith(openingBook: value);
-
-    debugPrint("$_tag openingBook: $value");
-  }
-
   void _setTone(Preferences _preferences, bool value) {
     LocalDatabaseService.preferences =
         _preferences.copyWith(toneEnabled: value);
@@ -181,40 +152,6 @@ class GameSettingsPage extends StatelessWidget {
     debugPrint("$_tag experimentsEnabled: $value");
   }
 
-  // Display
-  void _setLanguage(Display _display, Locale value) {
-    LocalDatabaseService.display = _display.copyWith(languageCode: value);
-
-    debugPrint("$_tag languageCode: $value");
-  }
-
-  void _setIsPieceCountInHandShown(Display _display, bool value) {
-    LocalDatabaseService.display =
-        _display.copyWith(isPieceCountInHandShown: value);
-
-    debugPrint("$_tag isPieceCountInHandShown: $value");
-  }
-
-  void _setIsNotationsShown(Display _display, bool value) {
-    LocalDatabaseService.display = _display.copyWith(isNotationsShown: value);
-
-    debugPrint("$_tag isNotationsShown: $value");
-  }
-
-  void _setIsHistoryNavigationToolbarShown(Display _display, bool value) {
-    LocalDatabaseService.display =
-        _display.copyWith(isHistoryNavigationToolbarShown: value);
-
-    debugPrint("$_tag isHistoryNavigationToolbarShown: $value");
-  }
-
-  void _setStandardNotationEnabled(Display _display, bool value) {
-    LocalDatabaseService.display =
-        _display.copyWith(standardNotationEnabled: value);
-
-    debugPrint("$_tag standardNotationEnabled: $value");
-  }
-
   Column _buildPrefs(BuildContext context, Box<Preferences> prefBox, _) {
     final Preferences _preferences = prefBox.get(
       LocalDatabaseService.preferencesKey,

src/ui/flutter_app/lib/screens/rule_settings/rule_settings_page.dart

@@ -193,12 +193,7 @@ class RuleSettingsPage extends StatelessWidget {
     debugPrint("[config] mayRemoveMultiple: $value");
   }
 
-  // Unused
-  void _setNPiecesAtLeast(Rules _rules, int value) {
-    LocalDatabaseService.rules = _rules.copyWith(piecesAtLeastCount: value);
 
-    debugPrint("[config] piecesAtLeastCount: $value");
-  }
 
   Widget _buildRules(BuildContext context, Box<Rules> rulesBox, _) {
     final Rules _rules = rulesBox.get(

src/ui/flutter_app/lib/services/engine/engine.dart

@@ -16,7 +16,6 @@
   along with this program.  If not, see <http://www.gnu.org/licenses/>.
 */
 
-import 'package:flutter/material.dart';
 import 'package:sanmill/mill/position.dart';
 
 enum EngineType {