Delete ClassHelper and fix compaction bug in GetDirectInterface

Cleanup helps to prevent compaction bugs. Fixed a fairly serious
compaction error caused by calling ClassHelper::GetDirectInterface
without handling the case where it causes thread suspension due to
ResolveType.

Bug: 8981901

Change-Id: I82b3bb6dd48d21eb6ece7aae0733c4a23c2bc408
diff --git a/oatdump/oatdump.cc b/oatdump/oatdump.cc
index fef25e0..aaf9ed5 100644
--- a/oatdump/oatdump.cc
+++ b/oatdump/oatdump.cc
@@ -1147,7 +1147,7 @@
         state->stats_.ComputeOutliers(total_size, expansion, method);
       }
     }
-    state->stats_.Update(ClassHelper(obj_class).GetDescriptor(), object_bytes);
+    state->stats_.Update(obj_class->GetDescriptor().c_str(), object_bytes);
   }
 
   std::set<const void*> already_seen_;