It's pretty easy with a good DNS blocker. I use personalDNSfilter. You can block entire domains, of just specific hosts. It's got a console that shows you all the requests that happening in real-time so you can launch an app, and watch the console to see all the hosts it's contacting. What I do is start off blocking them all, then I carefully unblock one by one to arrive at the perfect config that allows the proper functioning of the app while blocking all the unnecessary shit.