Clean up LoggingTensor semantic (#72620)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/72620
Clarify how LoggingTensor works with autograd.
The updated comment should cover the semantic changes.
Test Plan: Imported from OSS
Reviewed By: samdow
Differential Revision: D34214956
Pulled By: albanD
fbshipit-source-id: 730d0a68f4228d2a84758e6807d869a34cbc1b31
(cherry picked from commit 66110bf16bbe17d52781d05077eb73192e0fe3c4)
