Put back ListIterator.remove() override.

It was erroneously removed in 0602bc.
ListIterator.remove() overrides default method
in Iterator and makes it abstract.

Change-Id: I22935cebda525c2a75da0ec4d90b4d91d478c59c

user/super/com/google/gwt/emul/java/util/ListIterator.java

diff --git a/user/super/com/google/gwt/emul/java/util/ListIterator.java b/user/super/com/google/gwt/emul/java/util/ListIterator.java
index 550027c..527cfe5 100644
--- a/user/super/com/google/gwt/emul/java/util/ListIterator.java
+++ b/user/super/com/google/gwt/emul/java/util/ListIterator.java
@@ -37,5 +37,8 @@
 
   int previousIndex();
 
+  @Override
+  void remove();
+
   void set(E o);
 }