Don't use private libraries.

[toots]

This PR removes the use of private libraries.

At the moment, dune does not generate valid META files when using private libraries: ocaml/dune#4839. The fix has been implemented in ocaml/dune#4841 but is currently waiting for a release: https://github.com/ocaml/dune/blob/main/CHANGES.md#unreleased

[toots]

Example of the issue:

#=== ERROR while compiling liquidsoap.2.1.0 ===================================#
# context              2.0.8 | linux/arm64 | ocaml-base-compiler.4.12.1 | pinned(git+file:///tmp/liquidsoap-full/liquidsoap#main#948278f1)
# path                 ~/.opam/4.12.1/.opam-switch/build/liquidsoap.2.1.0
# command              /usr/bin/make
# exit-code            2
# env-file             ~/.opam/log/liquidsoap-12-014b3e.env
# output-file          ~/.opam/log/liquidsoap-12-014b3e.out
### output ###
# [...]
# make[2]: Leaving directory '/home/opam/.opam/4.12.1/.opam-switch/build/liquidsoap.2.1.0/src/encoder_formats'
# make[2]: Entering directory '/home/opam/.opam/4.12.1/.opam-switch/build/liquidsoap.2.1.0/src'
# MENHIR tools/json_parser.mly
# MENHIR lang/parser.mly
# OCAMLDEP
# OCAMLOPT -c tools/log.mli
# ocamlfind: Package `errno_bindings' not found - required by `unix-errno.unix'
# make[2]: *** [../Makefile.rules:125: tools/log.cmi] Error 2

[psafont]

So that's what made some failures appear in the CI when merging the change to opam-repo.

Thanks for this, I'll cut a release with this changes and once it's fixed on a released dune I can bump the minimal version and make the libraries private again to reduce the chance of using them externally.

Do you think there are other worthwhile changes from your port to dune? I'd be happy to integrate them as well

[toots]

Thanks for the quick response! I'm not sure haha. I think this looks fine as is, except for this unfortunate bug.