Removing graphsurgeon optional dependency, improving import error rep…
This pull request **introduces 1 alert** when merging 3afd577d38d6304614bfc59b57beae7f58e2679f into b6bdccd4effef234b7cb44917d57f1368b9b23d9 - [view on LGTM.com](https://lgtm.com/projects/g/NVIDIA/NeMo/rev/pr-cc87bcbdf4417483b27b2f378f45917a0f3961e2)

**new alerts:**

* 1 for Unused import
…orting
I did not remove graph surgeon install from Dockerfile - as it's nice to have anyway and maybe some users already use it.
But I did remove the extra GS step on export.