Chore: remove unused data field from ListNode class

Author: Dlafferty251

lesson_12/structs_java/structs_app/src/main/java/com/codedifferently/lesson12/ListNode.java

@@ -3,7 +3,6 @@
 public class ListNode {
   int val;
   ListNode next;
-  int data;
 
   ListNode() {}