Revert "[dynamo] Activation checkpointing as higher order op (#101028)"
This reverts commit de15e740a1f1cf0f267bb77ef851522ce2ab4674.
Reverted https://github.com/pytorch/pytorch/pull/101028 on behalf of https://github.com/jeanschmidt due to breaking internal builds ([comment](https://github.com/pytorch/pytorch/pull/101028#issuecomment-1548280970))
