Fix compilation on OCaml 5.0 without ocamlfind installed

[kit-ty-kate]

#=== ERROR while compiling base64.3.5.0 =======================================#
# context              2.1.2 | linux/x86_64 | ocaml-variants.5.0.0+trunk | file:///home/opam/opam-repository
# path                 ~/.opam/5.0/.opam-switch/build/base64.3.5.0
# command              ~/.opam/opam-init/hooks/sandbox.sh build dune build -p base64 -j 31
# exit-code            1
# env-file             ~/.opam/log/base64-19-b34c70.env
# output-file          ~/.opam/log/base64-19-b34c70.out
### output ###
# File "src/dune", line 5, characters 12-17:
# 5 |  (libraries bytes))
#                 ^^^^^
# Error: Library "bytes" not found.
# -> required by library "base64" in _build/default/src
# -> required by _build/default/META.base64
# -> required by _build/install/default/lib/base64/META
# -> required by _build/default/base64.install
# -> required by alias install
# File "src/dune", line 14, characters 12-17:
# 14 |  (libraries bytes))
#                  ^^^^^
# Error: Library "bytes" not found.
# -> required by library "base64.rfc2045" in _build/default/src
# -> required by _build/default/META.base64
# -> required by _build/install/default/lib/base64/META
# -> required by _build/default/base64.install
# -> required by alias install

The reason is that dune does not have the bytes builtin when compiling with OCaml 5.0 anymore. It might be a dune bug though but in any case it’s good to remove unnecessary dependencies which can make the compilation of base64 brittle with some combination of dune version and concurrent ocamlfind installation.

[kit-ty-kate]

All green (except s390x but this can be ignored)

[copy]

Gently pinging @dinosaure to merge.

[dinosaure]

Thanks, I will cut a release next week.