Rollup merge of #89068 - bjorn3:restructure_rt2, r=joshtriplett

Restructure std::rt (part 2)

A couple more cleanups on top of https://github.com/rust-lang/rust/pull/89011

Blocked on #89011

library/std/src/io/mod.rs

@@ -299,9 +299,7 @@ mod util;
 
 const DEFAULT_BUF_SIZE: usize = crate::sys_common::io::DEFAULT_BUF_SIZE;
 
-pub(crate) fn cleanup() {
-    stdio::cleanup()
-}
+pub(crate) use stdio::cleanup;
 
 struct Guard<'a> {
     buf: &'a mut Vec<u8>,