Remove code left unused by in-memory build file writes

Since #9170 writes build files through Build_file_store, nothing writes
or reads them through channels any more. make dead-code reported:

- Misc.output_to_bin_file_directly, Ext_buffer.output_buffer and
  Cmi_format.read_cmi_channel: never used; removed.
- File_util.read_build_file: used only inside File_util; no longer
  exported.
- Compiler_process.run_requests: its ?poll and ?on_complete are never
  passed (the only caller is a test); removed, like the other
  never-passed optional arguments.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01Kbf3gLDo8mBJKpNE25WAwT
Signed-off-by: Christoph Knittel <ck@cca.io>

Author: cknitt

compiler/ext/ext_buffer.ml

@@ -108,8 +108,6 @@ let add_string_char b s c =
    really_input ic b.buffer b.position len;
    b.position <- b.position + len *)
 
-let output_buffer oc b = output oc b.buffer 0 b.position
-
 (**
    It could be one byte, two bytes, three bytes and four bytes 
    TODO: inline for better performance

compiler/ext/ext_buffer.mli

@@ -76,8 +76,4 @@ val add_string : t -> string -> unit
     Raise [End_of_file] if the channel contains fewer than [n]
     characters. *)
 
-val output_buffer : out_channel -> t -> unit
-(** [output_buffer oc b] writes the current contents of buffer [b]
-    on the output channel [oc]. *)
-
 val add_string_char : t -> string -> char -> unit

compiler/ext/misc.ml

@@ -113,19 +113,6 @@ let create_hashtable init =
   Array.iter (fun (key, data) -> Hashtbl.add tbl key data) init;
   tbl
 
-(* File copy *)
-
-let output_to_bin_file_directly filename fn =
-  let filename = Compiler_request_state.resolve_path filename in
-  let oc = open_out_bin filename in
-  match fn filename oc with
-  | v ->
-    close_out oc;
-    v
-  | exception e ->
-    close_out oc;
-    raise e
-
 (* Integer operations *)
 
 module Int_literal_converter = struct

compiler/ext/misc.mli

@@ -61,8 +61,6 @@ val create_hashtable : ('a * 'b) array -> ('a, 'b) Hashtbl.t
 (* Create a hashtable of the given size and fills it with the
    given bindings. *)
 
-val output_to_bin_file_directly : string -> (string -> out_channel -> 'a) -> 'a
-
 module Int_literal_converter : sig
   val int : string -> int
 end

compiler/ml/cmi_format.ml

@@ -52,14 +52,6 @@ let check_magic_number filename buffer =
       raise (Error (Wrong_version_interface (filename, "an older")))
     else raise (Error (Not_an_interface filename))
 
-let read_cmi_channel filename ic =
-  try
-    check_magic_number filename
-      (really_input_string ic (String.length Config.cmi_magic_number));
-    input_cmi ic
-  with End_of_file | Failure _ -> raise (Error (Corrupted_interface filename))
-
-(* The same as [read_cmi_channel] on a channel holding [contents]. *)
 let read_cmi_contents filename contents =
   let magic_length = String.length Config.cmi_magic_number in
   if String.length contents < magic_length then

compiler/ml/cmi_format.mli

@@ -29,7 +29,6 @@ val input_cmi : in_channel -> cmi_infos
 
 (* read a cmi from a filename, checking the magic *)
 val read_cmi : string -> cmi_infos
-val read_cmi_channel : string -> in_channel -> cmi_infos
 
 val read_cmi_contents : string -> string -> cmi_infos
 (** [read_cmi_contents filename contents] reads an interface from the

rewatch-ocaml/compiler_process.ml

@@ -110,8 +110,7 @@ let run_tasks ?poll ?on_complete tasks =
     ~max_jobs:(Compiler_execution_mode.configured_count ())
     ?poll ?on_complete tasks
 
-let run_requests ?poll ?on_complete requests =
-  requests |> List.map task |> run_tasks ?poll ?on_complete
+let run_requests requests = requests |> List.map task |> run_tasks
 
 let parse_request ~build_dir ~(config : Config.t) path =
   let ast = Source.ast_path path in

rewatch-ocaml/compiler_process.mli

@@ -8,11 +8,7 @@ type request = {args: string list; cwd: string}
 val parse_request : build_dir:string -> config:Config.t -> string -> request
 val run : ?poll:(unit -> unit) -> request -> Process.result
 
-val run_requests :
-  ?poll:(unit -> unit) ->
-  ?on_complete:(int -> unit) ->
-  request list ->
-  Process.result list
+val run_requests : request list -> Process.result list
 
 val publish_parse :
   build_dir:string -> ocaml_dir:string -> config:Config.t -> string -> unit

rewatch-ocaml/file_util.mli

@@ -17,10 +17,6 @@ val exists : string -> bool
 val files_equal : string -> string -> bool
 val copy_file_if_different : string -> string -> bool
 
-val read_build_file : string -> string
-(** Reads a build file through [Build_file_store]. A missing file raises
-    [Unix.Unix_error ENOENT]. *)
-
 val write_build_file : ?keep:bool -> string -> string -> unit
 val copy_build_file : ?keep:bool -> string -> string -> unit