tanh_backward: Port to structured (#60816)
Summary: Pull Request resolved: https://github.com/pytorch/pytorch/pull/60816
Test Plan: Imported from OSS
Reviewed By: mruberry
Differential Revision: D29449375
Pulled By: ezyang
fbshipit-source-id: 93b70341fc6a2a42056fef74d6e5d81ec34e9da2
