remove clone method

app/src/main/java/org/cutem/lab2/CalendarDate.java

@@ -5,7 +5,7 @@ package org.cutem.lab2;
  * 1. A constructor that can return a CalendarDate object through the given string.
  * 2. A method named getDayOfWeek() that can get the index of a day in a week.
  */
-public class CalendarDate implements Cloneable {
+public class CalendarDate {
     private int year;
     private int month;
     private int day;
@@ -113,14 +113,4 @@ public class CalendarDate implements Cloneable {
         return year + month + day;
     }
 
-    @Override
-    public Object clone() {
-        try {
-            return super.clone();
-        } catch (CloneNotSupportedException e) {
-            // impossible to happen
-            throw new InternalError(e);
-        }
-    }
-
 }