ObjPtr<>-ify array allocations.

And remove some unnecessary calls to ObjPtr<>::Ptr().

Test: m test-art-host-gtest
Test: testrunner.py --host --optimizing
Bug: 31113334
Change-Id: Ie313980f7f23b33b0ccea4fa8d5131d643c59080
diff --git a/runtime/native/java_lang_Class.cc b/runtime/native/java_lang_Class.cc
index c6bdfa1..82e54e2 100644
--- a/runtime/native/java_lang_Class.cc
+++ b/runtime/native/java_lang_Class.cc
@@ -646,8 +646,8 @@
         soa.Decode<mirror::Class>(WellKnownClasses::java_lang_annotation_Annotation__array);
     ObjPtr<mirror::ObjectArray<mirror::Object>> empty_array =
         mirror::ObjectArray<mirror::Object>::Alloc(soa.Self(),
-                                                   annotation_array_class.Ptr(),
-                                                   0);
+                                                   annotation_array_class,
+                                                   /* length */ 0);
     return soa.AddLocalReference<jobjectArray>(empty_array);
   }
   return soa.AddLocalReference<jobjectArray>(annotations::GetAnnotationsForClass(klass));