Outdated sample projects. Update to GPGS v2.

[obigu]

Please, update the samples to GPGS V2 (play-services-games-v2).

There are no samples using Play Game Services v2 and were last updated 3 years ago.

The current Google Play Game Services documentation such as https://developers.google.com/games/services/android/achievements is pointing to this repository to find sample implementations.