Do not install rebar bundled with elixir

Author: ericmj

lib/mix/lib/mix/tasks/local.rebar.ex

@@ -18,16 +18,11 @@ defmodule Mix.Tasks.Local.Rebar do
   def run(argv) do
     {_, argv, _} = OptionParser.parse(argv)
     do_install(case argv do
-      []       -> rebar_path
+      []       -> @rebar_url
       [path|_] -> path
     end)
   end
 
-  defp rebar_path do
-    bundled_with_elixir = Path.join(:code.lib_dir(:mix), "../../rebar")
-    if File.regular?(bundled_with_elixir), do: bundled_with_elixir, else: @rebar_url
-  end
-
   defp do_install(path) do
     rebar = Mix.Utils.read_path!(path)
     local_rebar_path = Mix.Rebar.local_rebar_path