This was the remove method we wrote in class without using the dummy nodes
at the front and back of the list. On the exam that you will not have a back
field to worry about and it won't be a doubly-linked list (with next and
prev references), it will only be singly-linked (with next references).

When I tried to write this code, I made mistakes until I took it slowly
and drew pictures.  Please draw pictures when you study and take the exam!


      if (index == 0) {
         front = front.next;
         if (front != null) {
            front.prev = null;
         }
      } else {
         ListNode current = nodeAt(index - 1);
         current.next = current.next.next;
         if (current.next != null) {
            current.next.prev = current;
         }
      }
      if (index == size - 1) {
         back = back.prev;
      }
      size--;