Merge "Remove unnecesaary constants of Session2Command"

    public abstract static class SessionCallback {

        /**

         * Called when a controller is created for this session. Return allowed commands for

         * controller. By default it allows all connection requests and commands.

         * controller. By default it returns {@code null}.

         * <p>

         * You can reject the connection by returning {@code null}. In that case, controller

         * receives {@link MediaController2.ControllerCallback#onDisconnected(MediaController2)}

        @Nullable

        public Session2CommandGroup onConnect(@NonNull MediaSession2 session,

                @NonNull ControllerInfo controller) {

            Session2CommandGroup commands = new Session2CommandGroup.Builder()

                    .addAllPredefinedCommands(Session2Command.COMMAND_VERSION_1)

                    .build();

            return commands;

            return null;

        }

        /**