remove dangerous code in GameCenter clearAllScores
remove dangerous code in GameCenter clearAllScores

it's not safe to simply submit 0 as new score. just think of scores sorted from
low to high. the user would jump straight to the top - no good!

hovergames/avalon,Lt-Red/avalon,hovergames/avalon,Lt-Red/avalon,Lt-Red/avalon,hovergames/avalon