I ran into the same issue a few months ago.
You have to go to My Trips on aa.com and remove them from the list there. Then refresh your app and they will be gone.
That doesn't work. In my case the reservations are gone from the website but they're still there on the app after several months. There doesn't appear to be a solution for this one...
https://www.flyertalk.com/forum/28674109-post312.html