Made DequeIterator private
Test 10: Check iterator() after intermixed calls to addFirst(), addLast(), removeFirst(), and removeLast()
      -  student   solution has 2 non-null entries
      -  reference solution has 1 non-null entries
      -  1 extra entry in student solution: 3
      iterator failed after applying operation 5
Fixed the removeFirst method to make null all the references to the objects removed.
Changes to fix the error.
The test case wasn't able to reproduce it, so I'm hopping this changes solves it
java.lang.ArrayIndexOutOfBoundsException: 0
     RandomizedQueue.enqueue(RandomizedQueue.java:39)