Related to: spring-projects/spring-integration#9362

After the fix in Spring Integration: spring-projects/spring-integration@bdcb856
we ended up in a deadlock situation with a `beginPublishingTrigger` in the `FunctionConfiguration`
used for the `delaySubscription()` on an original `Publisher`.
The `FluxMessageChannel` uses its own `delaySubscription()` until the channel has its subscribers.
Apparently the logic before was with errors, so the `FluxMessageChannel` was marked as active
even if its subscriber is not ready yet, leading to famous `Dispatcher does not have subscribers` error.
So, looks like this `beginPublishingTrigger` was introduced back in days in Spring Cloud Stream
to mitigate that situation until we really emit a `BindingCreatedEvent`.

The deadlock (and the flaw, respectively) is with the `setupBindingTrigger()` method implementation
where `FluxMessageChannel` now "really" delays a subscription to the provided `Publisher`,
therefore not triggering that `Mono.create()` fulfilment immediately.
The `BindingCreatedEvent` arrives earlier, than we have a subscriber on the channel,
but `triggerRef.get()` is `null`, so we don't `success()` it and in the end don't subscribe
to an original `Publisher` since `delaySubscription()` on it is never completed.

Since `FunctionConfiguration` fully relies on `IntegrationFlow.from(Publisher)`,
which ends up with the mentioned  `FluxMessageChannel.subscribeTo()` and its own `delaySubscription()`
(which, in turn, apparently fixed now), we don't need our own `delaySubscription()` any more.
Therefore the fix in this PR is to propose to remove `beginPublishingTrigger` logic altogether.