Updating update_database.ml for OCaml 5

[aqjune]

HOL Light is mostly working okay on OCaml 5, but features that require update_database.ml are still missing.

The placeholder file is here: https://github.com/jrh13/hol-light/blob/master/update_database_5.ml

[SnarkBoojum]

I had a look and pa_j.ml also needs an update.