Be clearer that not all aborting ends with an "AbortError" DOMException

[annevk]

I saw a thread on Twitter between @LeaVerou and @jyasskin that highlighted the current text only addresses APIs yielding promises. I'm not sure there is precedent for event-based APIs, where we might want to dispatch an abort event or some such, but we could at least discuss addEventListener(), which effectively silently removes listeners.