Port `cumprod` kernel to structured kernels. (#61899)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/61899
Tracking issue: #55070
This PR also removes `at::_cumprod`, which was the "backend" for `at::cumprod`.
Test Plan: Imported from OSS
Reviewed By: ejguan
Differential Revision: D29939489
Pulled By: ezyang
fbshipit-source-id: d5e4a6dfa6c79e4b135508ea13c2d11bd0684f63
