Revert "add OpamConsole.Tree.to_json"

This reverts commit c56c506.

src/core/opamConsole.ml

@@ -1102,17 +1102,6 @@ module Tree = struct
     Buffer.add_char buff '\n';
     go_children "" children;
     msg "%s" (Buffer.contents buff)
-
-  let rec to_json ?(flatten=false) ~encoder { value; children } : OpamJson.t =
-    let fields =
-      match children with
-      | [] -> []
-      | _ -> ["children", `A (List.map (to_json ~flatten ~encoder) children)]
-    in
-    match flatten, encoder value with
-    | false, value -> `O (("value", value) :: fields)
-    | true, `O fields' -> `O (fields' @ fields)
-    | _, _ -> invalid_arg "encoder returned a non-object value"
 end
 
 (* This allows OpamStd.Config.env to display warning messages *)

src/core/opamConsole.mli

@@ -179,8 +179,4 @@ module Tree : sig
   (** Prints the given tree as a Unicode/ASCII art.
     @param printer may return a multi-line string, but should not return an empty string. *)
   val print: ?symbols:symbols -> printer:('a -> string) -> 'a t -> unit
-
-  (** Encodes the given tree as JSON.
-    @param encoder must return [`O fields] when [~flatten:true]. *)
-  val to_json: ?flatten:bool -> encoder:('a -> OpamJson.t) -> 'a t -> OpamJson.t
 end