Remove save overwrite

[mvpatel2000]

What does this PR do?

Previously, we required save_overwrite=False as it was not clear if a user intended to overwrite or resume from a checkpoint.

However, it turns out this situation is well defined. Autoresume = resume from symlink file. It is a transformation on load_path, and nothing else. So, you can actually set autoresume on and save_overwrite to True, which would be useful for partial checkpoint uploads where the symlink file is not added.

[mvpatel2000]

Need approval from either Ning or Evan. Did we not test that save_overwrite=True and autoresume=True threw an error before?

We did, I removed test

[eracah]

oh too late