cull(engine-cleanup): pass-8 phase-2 cascade round 1

[trim] fully-unreachable files deleted: 6
[trim] files edited: 55, files deleted: 0, nodes removed: 244
[type-trim] files edited: 1, types removed: 1

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

SVSim.BattleEngine/Engine/ClassCharaPrm.cs

@@ -102,8 +102,6 @@ public class ClassCharaPrm
 		}
 	};
 
-	private int _defaultCharaId;
-
 	private int _currentCharaId;
 
 	private int ClassCharaLv;