dedup _get_model_external_data_paths (#2217)
* dedup _get_model_external_data_paths
* Update optimum/onnx/utils.py
* make style
---------
Co-authored-by: Hualiang Xie (from Dev Box) <hualxie@microsoft.com>
Co-authored-by: Ilyas Moutawwakil <57442720+IlyasMoutawwakil@users.noreply.github.com>
