doc: revise AbortSignal text and example using events.once()

Add a line to the example code to clarify what happens if an event is
emitted after listening is canceled. Make minor revisions to surrounding
text.

PR-URL: #35005
Backport-PR-URL: #38386
Reviewed-By: Michaël Zasso <[email protected]>
Reviewed-By: Benjamin Gruenbaum <[email protected]>
Reviewed-By: Anna Henningsen <[email protected]>

Author: Trott

doc/api/events.md

@@ -839,8 +839,7 @@ added:
 * `emitter` {EventEmitter}
 * `name` {string}
 * `options` {Object}
-  * `signal` {AbortSignal} An {AbortSignal} that may be used to cancel waiting
-    for the event.
+  * `signal` {AbortSignal} Can be used to cancel waiting for the event.
 * Returns: {Promise}
 
 Creates a `Promise` that is fulfilled when the `EventEmitter` emits the given
@@ -899,7 +898,7 @@ ee.emit('error', new Error('boom'));
 // Prints: ok boom
 ```
 
-An {AbortSignal} may be used to cancel waiting for the event early:
+An {AbortSignal} can be used to cancel waiting for the event:
 
 ```js
 const { EventEmitter, once } = require('events');
@@ -922,6 +921,7 @@ async function foo(emitter, event, signal) {
 
 foo(ee, 'foo', ac.signal);
 ac.abort(); // Abort waiting for the event
+ee.emit('foo'); // Prints: Waiting for the event was canceled!
 ```
 
 ### Awaiting multiple events emitted on `process.nextTick()`