The FM Radio app has been a staple of Windows phones for years. The feature dates back to the days of the Zune.
For the people that have grown to love the feature, you may want to stay away from the latest Fast ring build, Windows 10 Mobile build 14322, as the app has been removed.
We checked on a Lumia 535, 550, 640, 650, 830, 930, and 950. On build 14322, there's no FM Radio app on any of them.
Oddly enough, this seems to be one of the few stock apps that's not even available in the Store. There is, however, a third party FM Radio app that you can grab right here.
We've reached out to Microsoft for comment, but as of right now, have no way of knowing if the FM Radio app will return.
Source: Windows Central