[ONNX] Remove static None graph output (#82623)
Fixes #82370
* Unify the export behavior regarding static None outputs. These are
dropped for both traced graph and TorchScript graph export.
* `Optional` outputs are not affected.
Fixes #82370
Pull Request resolved: https://github.com/pytorch/pytorch/pull/82623
Approved by: https://github.com/AllenTiTaiWang, https://github.com/abock
