[c10d] s/torch::autograd::variable/at::Tensor/g (#54763)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/54763
Replaces deprecated torch::autograd::variable with at::Tensor.
torch::autograd::variable is defined as equal to at::Tensor now so this should
be a noop, but follows convention of using tensor instead of Variable.
ghstack-source-id: 125040109
Test Plan: CI
Reviewed By: SciPioneer
Differential Revision: D27356450
fbshipit-source-id: 1a001358d7726a597141ec47803c8213db4814c0
