remove package.exs, use mix branch instead

package.exs

@@ -1,30 +0,0 @@
-defmodule JSX.Mixfile do
-use Mix.Project
-
-  def project do
-    [
-      app: :jsx,
-      version: "2.3.0",
-      description: "an erlang application for consuming, producing and manipulating json. inspired by yajl",
-      package: package
-    ]
-  end
-
-  defp package do
-    [
-      files: [
-        "CHANGES.md",
-        "LICENSE",
-        "package.exs",
-        "README.md",
-        "rebar.config",
-        "rebar.config.script",
-        "config",
-        "src"
-      ],
-      contributors: ["alisdair sullivan"],
-      links: %{"github" => "https://github.com/talentdeficit/jsx"},
-      licenses: ["MIT"]
-    ]
-  end
-end