Remove the infer-timestamp direction, at least temporarily

[NathanReb]

The --direction=infer-timestamp is not working very well. In particular it can't be used in dune because dune copies all the files to the _build directory first and therefore messes with the timestamps.

While I like the idea of having such an option, I'm quite struggling to find a good workflow for it outside of dune and its promotion mechanism.

I'd suggest we simply remove it for now until we have that figured out.

Note that if anyone's actually using this option and has a good workflow to integrate it outside of dune I'd love to hear about it. If that were the case an alternative would be to remove it from ocaml-mdx rule at least so that it only produces options that actually work fine with dune.

[NathanReb]

This has been fixed!