Remove unneeded case

lib/koans/10_processes.ex

@@ -28,7 +28,6 @@ defmodule Processes do
   koan "A common pattern is to include the sender in the message, so that it can reply" do
     pid = spawn(fn -> receive do
                          {:hello, sender} -> send sender, :how_are_you?
-                         _ -> assert false
                       end
                  end)