Remove ALPN Muxer (#1965)

We never ended up using this and it makes it much harder to reason about the listeners.

An explanation: for the moment I separated out all of the listeners in the struct, even though one should suffice, because when I did it that way first I was hitting some really weird and hard to find intermittent behavior where it seemed like the listeners were getting crossed. So I re-did it this way with each listener very explicitly referenced. I'm happy to make a follow-up PR that attempts to combine them all into a single listener without hitting the issues I did, if desired, but at least doing it via a separate PR means that it won't be something with removing the ALPN muxer that is at fault.

internal/servers/worker/testing.go

@@ -68,7 +68,7 @@ func (tw *TestWorker) ProxyAddrs() []string {
 
 	for _, listener := range tw.b.Listeners {
 		if listener.Config.Purpose[0] == "proxy" {
-			tcpAddr, ok := listener.Mux.Addr().(*net.TCPAddr)
+			tcpAddr, ok := listener.ProxyListener.Addr().(*net.TCPAddr)
 			if !ok {
 				tw.t.Fatal("could not parse address as a TCP addr")
 			}