Check this post. You can see @benorenstein removed about 1500 lines of code which powered these missing trails.
The old trail maps (lists of links and things you should know at various experience levels) are available in markdown here: GitHub - thoughtbot/trail-map: Trails to help designers and developers learn various topics.
@derekprior and @Jared_Smith
Thank you providing the links and also the post. Helps me a lot.