Remove unused ExUnit references

lib/koans.ex

@@ -23,7 +23,6 @@ defmodule Koans do
     single_var = Blanks.replace(body, Macro.var(:answer, Koans))
     quote do
       def unquote(name)(answer) do
-        converted = {answer}
         unquote(single_var)
         :ok
       end

lib/meditate.ex

@@ -3,8 +3,6 @@ defmodule Mix.Tasks.Meditate do
   alias Options
 
   def run(args) do
-    ExUnit.start
-    Application.ensure_all_started(:ex_unit)
     Application.ensure_all_started(:elixir_koans)
     Code.compiler_options(ignore_module_conflict: true)
     Watcher.start