[functorch] remove some testing hacks (#83079)
I'm not sure why I called this a hack in the first place (perhaps I
wanted to use tree_map and pytrees didn't support namedtuples?). This PR
deletes some comments and the conversion from namedtuple -> tuple
(because that is unnecessary).
Pull Request resolved: https://github.com/pytorch/pytorch/pull/83079
Approved by: https://github.com/Chillee
