These just wrap regular std Sender/Receiver without providing any value. Serialize/Deserialize was implement manually for MsgSender/MsgReceiver to assert. Serde being amazing, it provides with annotations to not require the traits to be implemented on some enum variants and assert at runtime which functionally equivalent but less error-prone than the fake trait implementations.

Removing the rest of channel.rs is coming in a followup.

Differential Revision: https://phabricator.services.mozilla.com/D70021

[ghsync] From https://hg.mozilla.org/mozilla-central/rev/b0d79edece1314cc5962c1f625bdffb947419425