Deleting friends on Android appears to work differently from deleting friends on Apple (you can see how Apple players delete friends here). Until someone adds a comment outlining an easier way to do it, going on to Origin and blocking a friend you want to delete may be the best route for Android players.
To delete friends or remove pending invitations, one way to do this is to go to http://www.origin.com and log in with your Origin ID. Your ID will appear at the top right of the screen, and if you click or tap on it, you’ll be able to go to “My Account”. You’ll see a menu at the left of the page. Click or tap on privacy, and you’ll be where you need to be. Look for a big empty box headed “Block List”.
Take a look at your game and write down the exact user names of the players or pending invitations that you wish to get rid of. Add them to your “Block List” on the Privacy page, by entering the name in the space under the big white box and tapping or clicking “Block”. Do this for each person or invitation you want to eliminate. Then, go back to your game and check that it works (you may need to completely close it and open it again to allow it time to synchronize).
You can unblock anyone at any time – and then they’ll be able to send you an invitation again. Until then, though, they won’t even know you play the game!
Thanks to Tine for the advice on this!