you can do it using this script : https://gist.github.com/renestalder/c5b77635bfbec8f94d28 , login, go to your news feed settings -> unfollow -> scroll down all the way to the bottom of the list (it won't work unless you do this!), then copy paste the script into the developer console.

UPDATE: I had to run it a few times, somehow even though it logged that it had unfollowed all of the items, there were still ~40 left the 2nd time, 3 the 3rd time, at which point i just unfollowed the remaining friends/pages manually.