Log Message:
Updated devel/ocaml-lwt to version 5.7.0.

I've removed superfluous dependencies from the package. Upstream changes
are many, so I'll add only the ones that break API (for the rest, see
the CHANGES file in the distribution):

* Lwt_result.catch now takes a function (unit -> 'a t)
  rather than a promise ('a t).
* Remove the deprecated Lwt.result type (use Stdlib.result instead).
* Remove the deprecated Lwt.make_value and Lwt.make_result functions
  (use Ok and Error instead).
* Remove the deprecated and unsafe waiter_of_wakener
  (keep the waiter around when you create the wakener instead).
* Remove the deprecated Lwt_stream.on_termination and
  Lwt_stream.on_terminate (bind to Lwt_stream.closed instead).
* Remove the deprecated Lwt_stream.result type (use Stdlib.result instead).
* Remove the deprecated Lwt_stream.map_exn function (use wrap_exn instead).