BotToBot to use new DeliveryModes.Stream

[tracyboehrer]

Simplify BotToBot.Bot1 to use reply streaming.

// Forward whatever C2 sent to the channel until a result is returned.
var result = await channel.SendActivityForResultAsync<object>(
    turnContext.Activity,
    async (activity) =>
    {
        // Just repeat message to C2
        await turnContext.SendActivityAsync(MessageFactory.Text($"({channel.DisplayName}) {activity.Text}"), cancellationToken);
    },
    cancellationToken);

See #29