ART: Remove another unnecessary mutator lock annotation.

Missed in https://android-review.googlesource.com/198690 .

Change-Id: I56a6dfe1126315957658962d51290e3bfa873c79
diff --git a/runtime/handle.h b/runtime/handle.h
index 5df010b..a415373 100644
--- a/runtime/handle.h
+++ b/runtime/handle.h
@@ -74,8 +74,7 @@
     return reference_;
   }
 
-  ALWAYS_INLINE const StackReference<mirror::Object>* GetReference() const
-      SHARED_REQUIRES(Locks::mutator_lock_) {
+  ALWAYS_INLINE const StackReference<mirror::Object>* GetReference() const {
     return reference_;
   }