Revert "[functorch] Refactor life handle storage (#90317)"
This reverts commit 4d494986af5201a0c487a9b7f3c68cfa6c4e28d0.
Reverted https://github.com/pytorch/pytorch/pull/90317 on behalf of https://github.com/osalpekar due to Causing contbuilds to fail when pytorch is built with -Wsign-compare internally - details in [D42019543](https://www.internalfb.com/diff/D42019543)
