better undo

app/src/main/java/chess/model/Piece.java

@@ -4,12 +4,10 @@ public abstract class Piece {
 
 	private final Color color;
 	private int moved;
-	private int ejectedMoveNumber;
 
 	public Piece(Color color) {
 		this.color = color;
 		this.moved = 0;
-		this.ejectedMoveNumber = -1;
 	}
 
 	public void move() {
@@ -28,18 +26,6 @@ public abstract class Piece {
 		this.moved--;
 	}
 
-	public boolean isEjected() {
-		return this.ejectedMoveNumber != -1;
-	}
-
-	public int getEjectedMoveNumber() {
-		return ejectedMoveNumber;
-	}
-
-	public void eject(int moveNumber) {
-		this.ejectedMoveNumber = moveNumber;
-	}
-
 	public abstract <T> T accept(PieceVisitor<T> visitor);
 
 }