Android O includes a variety of system changes. The persistent notifications "X is running in the background" or "apps are running in the background" are one of these changes. Unfortunately, there is no built-in option to whitelist apps which are OK.
The purpose of this app is to remove such a boring persistent notification. Keep the app installed and such annoying notifications will never appear again.
In Rubber: erase "running in the background" notifs 1.0.0This is the first version. Enjoy!