Revert "PyTorch -> C++17 (#98209) (#100557)"
This reverts commit 083f88e12632059e7e710634fc8708c8205678d5.
Reverted https://github.com/pytorch/pytorch/pull/100557 on behalf of https://github.com/jeanschmidt due to breaking internal builds ([comment](https://github.com/pytorch/pytorch/pull/100557#issuecomment-1543285863))
