Delete test that ensures correct version in mix.exs

The version is toggled between using the GitHub dependency for
development and the version number for stable releases. Since the test
was checking for the version number, it would fail when using GitHub for
the dependency.

installer/test/phx_new_test.exs

@@ -25,7 +25,6 @@ defmodule Mix.Tasks.Phx.NewTest do
 
       assert_file "phx_blog/README.md"
       assert_file "phx_blog/mix.exs", fn file ->
-        assert file =~ ~s[:phoenix, "~> #{Application.spec(:phx_new, :vsn)}"]
         assert file =~ "app: :phx_blog"
         refute file =~ "deps_path: \"../../deps\""
         refute file =~ "lockfile: \"../../mix.lock\""