Remove explicit deref workaround in dtor-order test. No longer necessary.

Author: froystig

src/test/run-pass/destructor-ordering.rs

@@ -18,7 +18,7 @@ state obj order_tracker(mutable int init) {
 
 obj dorder(@order_tracker tracker, int order, str message) {
   drop {
-    (*tracker).assert_order(order, message);
+    tracker.assert_order(order, message);
   }
 }