Some work in GameClient.h
[cosmetic] Clean up game info tags. Also fixes bug in CGameInfoTagLoader::GetPlatformInfoByExtension()
General game clients cleanup
Remove EnvironmentSetPerformanceLevel() Game API callback (replaced RETRO_ENVIRONMENT_SET_PERFORMANCE_LEVEL)
Make EnvironmentSetSupportNoGame() a Game API call instead of a callback

Also fixes typo with EnvironmentSetPixelFormat()