[PyTorch] Remove non-const TensorIterator::tensor() method (#55420)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/55420
It doesn't seem to be necessary, and it blocks using `c10::MaybeOwned` to support borrowing.
ghstack-source-id: 127092679
Test Plan: fitsships
Reviewed By: ezyang
Differential Revision: D27607270
fbshipit-source-id: a007e9896785c8708f8cc02035cc6f4607a0a31b
