Revert "Checkpoints Simplified (#2059)"

[dakinggg]

This reverts commit b25b7f0.

What does this PR do?

This reverts the refactor PR, which we are going to break up into individual PRs to fix the relevant issues. There will be four follow on PRs to fix:

1. the checkpoint download takes a long time, causing non zero ranks to timeout
2. autoresume + FSDP sharded checkpoints not working
3. skip the download on non local rank 0 ranks if not necessary
4. update dist timeout everywhere

What issue(s) does this change relate to?

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[eracah]

LGTM