Active Playlist can't be disabled or removed. Any lesson you open will be added to it automatically. You can't create/remove other playlist and adjust them, but not the Active one.

I ignore the active playlist entirely. It's not manageable because everything gets dumped in there regardless, even if I end up hating the content I listen to and never want to hear it again.. I couldn't find a way to manage it. Instead I just create my own playlists and manually add the things I wanted to those. It's a little work, but for me it's worth it to have dedicated playlists for the things I might want to listen to. So now it's easy for me to scroll to the right playlist and just listen to the one I want on repeat.

I know that doesn't help with how to actually get rid of the annoying active playlist situation, but that's how I have got around it. Ignoring it!