simplify decoded_rounds

[zamrokk]

type  player_action = ["Commit", an_action<bytes>] | ["Reveal", an_action<action>];
type round = {
    player1 : option<player_action>,
    player2 : option<player_action> 
};
type rounds = list<round<a>>
export type t = {
    players : [player, player]
    rounds,
    board : board,
    result : result,
    asleep : timestamp
};