Remove onBeginDispatchToListeners from CollectionReadyForBuildListener

I honestly can't remember why we needed this in the first place. But it
also conflicts with a few upcoming concepts:

- Notification batching (we might get multiple dispatchToListeners calls
before we get a single onBuildList call)
- Update debouncing (same issue)

So we're just going to remove it until we come up with a reason to want
it.

Test: atest SystemUITests
Change-Id: I47cb9c8b037af9daba64e1f59b20beddf138cce4
5 files changed