Rename XLAPreAutograd to AutogradXLA. (#43047)
Summary:
Fixes #{issue number}
Pull Request resolved: https://github.com/pytorch/pytorch/pull/43047
Reviewed By: ezyang
Differential Revision: D23134326
Pulled By: ailzhang
fbshipit-source-id: 5fcbc23755daa8a28f9b03af6aeb3ea0603b5c9a
