ART: Remove some unnecessary mutator lock annotations.

The StackReference<> pointer held by a Handle<> can be used
without holding the mutator lock. We already do that when
we copy Handle<>s around. Only accessing the actual content
of the pointed-to StackReference<> needs to be done while
holding the mutator lock.

Change-Id: I5f93bd7e277383192f1f16dff6883ecb26387414
diff --git a/runtime/entrypoints/quick/quick_trampoline_entrypoints.cc b/runtime/entrypoints/quick/quick_trampoline_entrypoints.cc
index 08c9b49..638fdb4 100644
--- a/runtime/entrypoints/quick/quick_trampoline_entrypoints.cc
+++ b/runtime/entrypoints/quick/quick_trampoline_entrypoints.cc
@@ -1779,8 +1779,7 @@
 
   void FinalizeHandleScope(Thread* self) SHARED_REQUIRES(Locks::mutator_lock_);
 
-  StackReference<mirror::Object>* GetFirstHandleScopeEntry()
-      SHARED_REQUIRES(Locks::mutator_lock_) {
+  StackReference<mirror::Object>* GetFirstHandleScopeEntry() {
     return handle_scope_->GetHandle(0).GetReference();
   }