games_previous.php: remove code when no game specified
games_previous.php: remove code when no game specified

This page has only ever been responsible for displaying a specific
game. The game list is now displayed on the `play_game.php` page.

smrealms/smr,hemberger/smr,smrealms/smr,hemberger/smr,hemberger/smr,hemberger/smr,smrealms/smr