Remove unused import.

src/main/java/edu/ntnu/stud/chaosgame/controller/game/GuiButtonController.java

@@ -30,7 +30,6 @@ import java.util.ArrayList;
 import java.util.List;
 import java.util.Objects;
 import javax.imageio.ImageIO;
-import javafx.scene.image.PixelWriter;
 import javafx.scene.image.PixelReader;
 import javafx.scene.paint.Color;