Revert "Add "last" setter to List."

sdk/lib/internal/list.dart

Index: sdk/lib/internal/list.dart
diff --git a/sdk/lib/internal/list.dart b/sdk/lib/internal/list.dart
index afba6cbd7be45e24516b8af06d77c0bd90722deb..473a87a622cc8b947c3b208c4928a84ef18fa85f 100644
--- a/sdk/lib/internal/list.dart
+++ b/sdk/lib/internal/list.dart
@@ -110,11 +110,6 @@ abstract class UnmodifiableListMixin<E> implements List<E> {
         "Cannot change the length of an unmodifiable list");
   }
 
-  void set last(E value) {
-    throw new UnsupportedError(
-        "Cannot modify an unmodifiable list");
-  }
-
   /** This operation is not supported by an unmodifiable list. */
   void setAll(int at, Iterable<E> iterable) {
     throw new UnsupportedError(