[BE] Do not package caffe2 in wheel (#87986)
If PyTorch is build without caffe2 integration, do not package unusable
.py files/headers
Same is true about functorch - don't package it unless building with `functorch` (although, I wonder if we should remove this option at some point in the future)
Followup after https://github.com/pytorch/builder/pull/1181
Pull Request resolved: https://github.com/pytorch/pytorch/pull/87986
Approved by: https://github.com/seemethere
