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/runtime/interpreter/interpreter_common.cc b/runtime/interpreter/interpreter_common.cc
index c5fb0d8..418aff5 100644
--- a/runtime/interpreter/interpreter_common.cc
+++ b/runtime/interpreter/interpreter_common.cc
@@ -117,8 +117,8 @@
                                        "Ljava/lang/VirtualMachineError;",
                                        "Invoking %s with bad arg %d, type '%s' not instance of '%s'",
                                        mh.GetName(), shorty_pos,
-                                       ClassHelper(o->GetClass()).GetDescriptor(),
-                                       ClassHelper(arg_type).GetDescriptor());
+                                       o->GetClass()->GetDescriptor().c_str(),
+                                       arg_type->GetDescriptor().c_str());
               return false;
             }
           }