I don't think there is such a thing. Someone has to provide the platform so that players can find each other and compete against each other (a matchmaking system, so to speak). This would then also be the "owner" of the casino and would have to ensure a license, even if the games take place between the players of the platform.
A licence is some sort of trust among gamblers to play on that particular casino but it doesn't imply that they cannot be scam as some of the other casinos have turned out to be scam even after owning a licence but still new legit casinos feel it obligatory to own a licence to increase the reputation and trust of gamblers before entering the market.The decentralisation of casino also required some kind of trust among gamblers to run and verify each bets or any other kind of system to make it smooth.