std: Remove old_io/old_path from the prelude

This commit removes the reexports of `old_io` traits as well as `old_path` types
and traits from the prelude. This functionality is now all deprecated and needs
to be removed to make way for other functionality like `Seek` in the `std::io`
module (currently reexported as `NewSeek` in the io prelude).

Closes #23377
Closes #23378

src/librustdoc/lib.rs

@@ -64,6 +64,8 @@ use std::path::PathBuf;
 use std::rc::Rc;
 use std::sync::mpsc::channel;
 
+#[allow(deprecated)] use std::old_path::Path;
+
 use externalfiles::ExternalHtml;
 use serialize::Decodable;
 use serialize::json::{self, Json};