fix: Remove ICEServer proxying from client to server (#400)

This made testing simple, but enabled insecure behavior. This allows
the listener to fetch ICEServers from a remote location, which will
likely be coderd.

agent/agent_test.go

@@ -95,7 +95,7 @@ func TestAgent(t *testing.T) {
 func setup(t *testing.T) proto.DRPCPeerBrokerClient {
 	client, server := provisionersdk.TransportPipe()
 	closer := agent.New(func(ctx context.Context) (*peerbroker.Listener, error) {
-		return peerbroker.Listen(server, &peer.ConnOptions{
+		return peerbroker.Listen(server, nil, &peer.ConnOptions{
 			Logger: slogtest.Make(t, nil),
 		})
 	}, &agent.Options{