Auto merge of #23470 - alexcrichton:less-prelude, r=aturon

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

diff --cc src/libcore/result.rs
Simple merge

diff --cc src/libstd/fs/mod.rs
Simple merge

diff --cc src/libstd/old_io/fs.rs
Simple merge

diff --cc src/libstd/sys/unix/fs.rs
Simple merge

diff --cc src/libstd/thread.rs
Simple merge