fix: Revert "add leading slash to Uri.to_path on windows"

This reverts commit 6d11e1a.

Author: rgrinberg

lsp/src/uri0.ml

@@ -46,7 +46,7 @@ let to_path t =
     |> String.replace_all ~pattern:"%3D" ~with_:"="
     |> String.replace_all ~pattern:"%3F" ~with_:"?"
   in
-  Filename.concat "/" path
+  if Sys.win32 then path else Filename.concat "/" path
 
 let of_path (path : string) =
   let path = Uri_lexer.escape_path path in