`escaped_path` was used by some users in 2.x, is missing in 3.0, and has no deprecation in 2.99

It was a private API so we didn't think users were using but some were, apparently:

https://twitter.com/plukevdh/status/491684829868875776

It would be good to add a deprecation warning to 2.99 for this since we missed it.
