[PyTorch] Reapply D25545777: Use .sizes() instead of .size() in _cat_out_cpu (#49761)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/49761
This was reverted because it landed in a stack together with
D25542799 (https://github.com/pytorch/pytorch/commit/9ce1df079f6ea90dd4b7f9aa12a1a78d51a8b204), which really was broken.
ghstack-source-id: 119361027
Test Plan: CI
Reviewed By: bwasti
Differential Revision: D25685855
fbshipit-source-id: b51f67ebe667199d15bfc6f8f131a6f1ab1b0352
