Cleanup copy methods (#11038)

* remove System.out.println
* Card copy() covariant return
* Effect copy() covariant return
* Cost copy() covariant return
* Ability copy() covariant return
* ContinuousEffect copy() covariant return

Mage/src/main/java/mage/abilities/keyword/SkulkAbility.java

@@ -22,7 +22,7 @@ public class SkulkAbility extends StaticAbility {
     }
 
     @Override
-    public Ability copy() {
+    public SkulkAbility copy() {
         return new SkulkAbility(this);
     }