How to remove find my iphone from an iPhone 5 without using the screen?

I have an iPhone 5 and I sold it on ebay for parts/not working and the person who purchased asked to remove "find my iPhone" from my iPhone by going on iCloud.com since my screen doesn't work.
How can I be able to do this if I have a second iPhone registered to the iCloud?

Sign on to icloud.com and you can remotely wipe it. He's right, if you sold it to him then you should do this, you should have done it before selling to him.