Shorten torch.fx.Node to Node (#2403)

Summary:
bypass-github-export-checks

Pull Request resolved: https://github.com/pytorch/executorch/pull/2403

It's too many characters to type out, and there was already a mix of switching between the two.

Doing this in a separate change to simplify review.
ghstack-source-id: 218520050
exported-using-ghexport

Reviewed By: SS-JIA

Differential Revision: D54859246

fbshipit-source-id: 4a5b57fe5c7ca760df42c9cef37d99f3794904e7