Update crossbeam-channel to v0.3

[stjepang]

On a popular request, I've changed the behavior of crossbeam-channel in v0.3 so that dropping all receivers disconnects the channel.

This means we don't need the channel library wrapper around crossbeam-channel anymore. Let's delete it.

Also note that now we can replace select! invocations like the following one with r.try_recv():

select! {
    recv(r, msg) => {},
    default => {},
}

We should update crossbeam-channel in ipc-channel, too.

I'd be happy to review PRs that update it to v0.3, just make sure to cc me!

cc @gterzian @SimonSapin @jdm

[Eijebong]

I might take a look at it next week if I find time. If anyone else want to work on that, feel free to do so though

[stjepang]

Implemented in #22142