Add pixel_shuffle to core aten decomps (#119899)
Summary: https://github.com/pytorch/pytorch/pull/118239 added a decomposition for pixel_shuffle, so pixel_shuffle no longer needs to be a Core ATen Op. We have also fixed the internal use case so that it no longer special cases on pixel_shuffle, allowing us to revert the changes in https://github.com/pytorch/pytorch/pull/118921.
Test Plan: CI
Differential Revision: D53766709
Pull Request resolved: https://github.com/pytorch/pytorch/pull/119899
Approved by: https://github.com/peterbell10, https://github.com/lezcano
