Remove Path.drop_prefix

not used anywhere

src/stdune/path.ml

@@ -502,12 +502,3 @@ let extension = Filename.extension
 
 let pp ppf t = Format.pp_print_string ppf (to_string t)
 
-let drop_prefix t ~prefix =
-  let t = to_string t in
-  let prefix =
-    to_string (
-      if String.is_suffix prefix ~suffix:"/" then
-        prefix
-      else
-        prefix ^ "/") in
-  String.drop_prefix t ~prefix

src/stdune/path.mli

@@ -137,14 +137,6 @@ val change_extension : ext:string -> t -> t
 
 val extension : t -> string
 
-(** maintains the invariant:
-    {[
-      let suffix = Option.value_exn (Path.drop_prefix t ~prefix) in
-      Path.relative prefix suffix = t
-    ]}
-*)
-val drop_prefix : t -> prefix:t -> string option
-
 val pp : Format.formatter -> t -> unit
 
 val build_dir_exists : unit -> bool