[refactor] Remove unnecessary declarations in command pattern.

command/src/main/java/com/iluwatar/Goblin.java

@@ -3,8 +3,8 @@ package com.iluwatar;
 public class Goblin extends Target {
 
 	public Goblin() {
-		this.setSize(Size.NORMAL);
-		this.setVisibility(Visibility.VISIBLE);
+		setSize(Size.NORMAL);
+		setVisibility(Visibility.VISIBLE);
 	}
 
 	@Override

command/src/main/java/com/iluwatar/InvisibilitySpell.java

@@ -4,10 +4,6 @@ public class InvisibilitySpell extends Command {
 
 	private Target target;
 
-	public InvisibilitySpell() {
-		target = null;
-	}
-
 	@Override
 	public void execute(Target target) {
 		target.setVisibility(Visibility.INVISIBLE);

command/src/main/java/com/iluwatar/ShrinkSpell.java

@@ -3,14 +3,8 @@ package com.iluwatar;
 public class ShrinkSpell extends Command {
 
 	private Size oldSize;
-
 	private Target target;
 
-	public ShrinkSpell() {
-		oldSize = null;
-		target = null;
-	}
-
 	@Override
 	public void execute(Target target) {
 		oldSize = target.getSize();

command/src/main/java/com/iluwatar/Wizard.java

@@ -5,9 +5,8 @@ public class Wizard extends Target {
 	private Command previousSpell;
 
 	public Wizard() {
-		this.setSize(Size.NORMAL);
-		this.setVisibility(Visibility.VISIBLE);
-		previousSpell = null;
+		setSize(Size.NORMAL);
+		setVisibility(Visibility.VISIBLE);
 	}
 
 	public void castSpell(Command command, Target target) {