Clean up mutexes on shutdown.

Change-Id: Ib961f954280c27f8858c4d6fb9010cc833bb28d2
diff --git a/src/class_linker.h b/src/class_linker.h
index 34ad9d7..90ac678 100644
--- a/src/class_linker.h
+++ b/src/class_linker.h
@@ -24,7 +24,9 @@
   // Initializes the class linker.
   static ClassLinker* Create(const std::vector<DexFile*>& boot_class_path);
 
-  ~ClassLinker() {}
+  ~ClassLinker() {
+    delete classes_lock_;
+  }
 
   // Finds a class by its descriptor name.
   // If class_loader is null, searches boot_class_path_.