Remove the dune warning on merlin

[Ninjapouet]

... when using a recent dune.

$ make
./scripts/before.sh build
opam exec -- dune build @install
File "dune-project", lines 4-46, characters 0-742:
 4 | (cram enable)
 5 | (name columns)
 6 | (allow_approximate_merlin)
....
44 |    ocamlformat
45 |   )
46 |  )
Warning: This field was deprecated in version 2.8 of the dune language. It is
useless since the Merlin configurations are not ambiguous anymore.

[Halbaroth]

How did you get this message? I tried to reproduce it but I got it only if I change the minimum version of dune language in dune-project for 2.8. My version of dune is 3.16.0.

It could be a bug in dune because there is a cram test to check that dune won't emit a warning if the dune language version is smaller than 2.7:
https://github.com/ocaml/dune/blob/main/test/blackbox-tests/test-cases/merlin/allow_approximate_merlin_warn.t/run.t