Delete deprecated formatted_ URL helper

The presence of this helper is causing the string `"Please pass format to the standard "` to appear 1364 separate times in the Ruby heap on the GitHub.com app.

This is in addition to the other strings that are retained in memory simply by defining this method.

We're not using it anywhere (and indeed, it'll just raise when you try to call it) so I'm thinking we should just delete it.

cc @github/rails @github/perf