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/mirror/object-inl.h b/runtime/mirror/object-inl.h
index bfebd5d..2d10b97 100644
--- a/runtime/mirror/object-inl.h
+++ b/runtime/mirror/object-inl.h
@@ -747,7 +747,7 @@
     } else {
       obj = GetFieldObject<Object>(field_offset);
     }
-    Runtime::Current()->RecordWriteFieldReference(this, field_offset, obj.Ptr(), true);
+    Runtime::Current()->RecordWriteFieldReference(this, field_offset, obj, true);
   }
   if (kVerifyFlags & kVerifyThis) {
     VerifyObject(this);