Remove output used only by sizes (#448) (#47665)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/47665
Re-enabled the pass to remove outputs from fusion that is only used by aten::size;
Added size computation for reduction op via new operator prim::ReductionSizes;
Test Plan: Imported from OSS
Reviewed By: navahgar, jamesr66a
Differential Revision: D25254675
Pulled By: Krovatkin
fbshipit-source-id: e9a057b0287ed0ac93b415647fd8e5e836ba9856
