avg_pool3d_backward: Port to structured (#59084)
Summary: Pull Request resolved: https://github.com/pytorch/pytorch/pull/59084
Test Plan: Imported from OSS
Reviewed By: ngimel
Differential Revision: D28802619
Pulled By: ezyang
fbshipit-source-id: 89a0fcdcf8976ca7c21da7a40fd26a1cba180faa
