[Composable] Use non-reentrant generator, remove reentrant (#105176)
Removes reentrant support for the composable checkpoint, as
non-reentrant is the recommended approach and we should use this when rolling
out composable checkpoint API.
Also removes the standalone implementation for non-reentrant and instead uses
the generator from below diff to reuse the original implemenetation.
Differential Revision: [D47451375](https://our.internmc.facebook.com/intern/diff/D47451375/)
Pull Request resolved: https://github.com/pytorch/pytorch/pull/105176
Approved by: https://github.com/awgu, https://github.com/fegin
