Remove unnecessary use of atomic-polyfill.

Only use it when CAS is actually needed.

embassy-net/Cargo.toml

@@ -51,7 +51,6 @@ generic-array = { version = "0.14.4", default-features = false }
 stable_deref_trait = { version = "1.2.0", default-features = false }
 futures = { version = "0.3.17", default-features = false, features = [ "async-await" ] }
 atomic-pool = "1.0"
-atomic-polyfill = "1.0.1"
 embedded-nal-async = { version = "0.3.0", optional = true }
 
 [dependencies.smoltcp]

embassy-net/src/tcp.rs

@@ -329,8 +329,8 @@ pub mod client {
     use core::cell::UnsafeCell;
     use core::mem::MaybeUninit;
     use core::ptr::NonNull;
+    use core::sync::atomic::{AtomicBool, Ordering};
 
-    use atomic_polyfill::{AtomicBool, Ordering};
     use embedded_nal_async::IpAddr;
 
     use super::*;