chore(nix): remove stdune dep from lsp

Signed-off-by: Rudi Grinberg <me@rgrinberg.com>

<!-- ps-id: 06f1c143-5c2c-4391-9c2f-802d21563080 -->

Author: rgrinberg

flake.nix

@@ -108,7 +108,6 @@
             propagatedBuildInputs = with pkgs.ocamlPackages; [
               jsonrpc
               yojson
-              stdune
               ppx_yojson_conv_lib
               uutf
             ];