message: Remove unused MultiDeviceIterator::lib_def_ member.
diff: @@ -392,7 +392,6 @@ class MultiDeviceIterator : public ResourceBase {
  const std::unique_ptr<FunctionHandleCache> function_handle_cache_;
  ResourceMgr resource_mgr_;
  CancellationManager cancellation_manager_;
  - std::shared_ptr<const FunctionLibraryDefinition> lib_def_ GUARDED_BY(mu_);
  int64 incarnation_id_ GUARDED_BY(mu_) = 0;
  std::unique_ptr<MultiDeviceBuffer> multi_device_buffer_ GUARDED_BY(mu_);
  