refactor(iroh): Remove with_cancel, use run_until_cancelled (#3000)

## Description

We manually created a function that was already provided by the
CancellationToken.  Use the one from the library for consistency.

## Breaking Changes

<!-- Optional, if there are any breaking changes document them,
including how to migrate older code. -->

## Notes & open questions

<!-- Any notes, remarks or open questions you have to make about the PR.
-->

## Change checklist

- [x] Self-review.
- [x] Documentation updates following the [style
guide](https://rust-lang.github.io/rfcs/1574-more-api-documentation-conventions.html#appendix-a-full-conventions-text),
if relevant.
- [x] Tests if relevant.
- [x] All breaking changes documented.

Author: flub

iroh/src/magicsock/relay_actor.rs

@@ -5,7 +5,6 @@
 
 use std::{
     collections::{BTreeMap, BTreeSet},
-    future::Future,
     net::{IpAddr, SocketAddr},
     sync::{atomic::Ordering, Arc},
     time::{Duration, Instant},
@@ -326,8 +325,8 @@ impl RelayActor {
                     match task_result {
                         Ok((url, ping_success)) => {
                             if !ping_success {
-                                with_cancel(
-                                    self.cancel_token.child_token(),
+                                let token = self.cancel_token.child_token();
+                                token.run_until_cancelled(
                                     self.close_or_reconnect_relay(&url, "rebind-ping-fail")
                                 ).await;
                             }
@@ -349,7 +348,8 @@ impl RelayActor {
                 }
                 _ = cleanup_timer.tick() => {
                     trace!("tick: cleanup");
-                    with_cancel(self.cancel_token.child_token(), self.clean_stale_relay()).await;
+                    let cancel_token = self.cancel_token.child_token();
+                    cancel_token.run_until_cancelled(self.clean_stale_relay()).await;
                 }
             }
         }
@@ -833,19 +833,6 @@ impl Iterator for PacketSplitIter {
     }
 }
 
-async fn with_cancel<F>(token: CancellationToken, f: F)
-where
-    F: Future<Output = ()>,
-{
-    tokio::select! {
-        _ = token.cancelled_owned() => {
-            // abort
-        }
-        _ = f => {
-        }
-    }
-}
-
 #[cfg(test)]
 mod tests {
     use super::*;