We don't need to remove index.html any more.

Since it's not a real file any longer, no need to worry about
removing it when we reset the dummy.

railties/lib/rails/generators/rails/plugin_new/plugin_new_generator.rb

@@ -107,7 +107,6 @@ def test_dummy_clean
         remove_file "Gemfile"
         remove_file "lib/tasks"
         remove_file "app/assets/images/rails.png"
-        remove_file "public/index.html"
         remove_file "public/robots.txt"
         remove_file "README"
         remove_file "test"