Removing attach_onnx_to_onnx
This pull request **introduces 1 alert** when merging 647a5bc614dcf01757efb363fabd1958b233e663 into bd6e1ff7a16e2cf0ec5c52df53d975df459cfe4e - [view on LGTM.com](https://lgtm.com/projects/g/NVIDIA/NeMo/rev/pr-2bdcfa9f3a865f559588bd10e67a3d2798937dcd)

**new alerts:**

* 1 for Unused import
Signed-off-by: Boris Fomitchev <bfomitchev@nvidia.com>