You might played few games on Google plus or reached few stages in game, For example 5th 6th stage in Angry Birds. Some time you might decide for various reason to start the game again or to remove them completely on your played game list.
Currently there is no such option where you can just remove all the games you played online on Google+ games. But you have an option to revoke access to the the games. Read here How to remove or revoke permission to a game on Google Plus. Let us know if you found the way to remove the played games on Google Plus games.