Clarify usage of eventHubFactory

app/assets/javascripts/helpers/event_hub_factory.js

 /**
  * An event hub with a Vue instance like API
  *
- * NOTE: There's an [issue open][4] to eventually remove this when some
- * coupling in our codebase has been fixed.
- *
  * NOTE: This is a derivative work from [mitt][1] v1.2.0 which is licensed by
  * [MIT License][2] © [Jason Miller][3]
  *
  * [1]: https://github.com/developit/mitt
  * [2]: https://opensource.org/licenses/MIT
  * [3]: https://jasonformat.com/
- * [4]: https://gitlab.com/gitlab-org/gitlab/-/issues/223864
  */
 class EventHub {
   constructor() {
@@ -91,9 +87,6 @@ class EventHub {
  * - $once
  * - $emit
  *
- * Please note, this was once implemented with `mitt`, but since then has been reverted
- * because of some API issues. https://gitlab.com/gitlab-org/gitlab/-/merge_requests/35074
- *
  * We'd like to shy away from using a full fledged Vue instance from this in the future.
  */
 export default () => {

doc/development/fe_guide/vue3_migration.md

@@ -37,32 +37,8 @@ If you need cross-component communication (between different Vue apps), then per
 
 **What to use instead**
 
-Vue documentation recommends using the [mitt](https://github.com/developit/mitt) library. It's relatively small (200 bytes, compressed) and has a clear API:
+We have created a factory that you can use to instantiate a new [mitt](https://github.com/developit/mitt)-like event hub.
 
-```javascript
-import mitt from 'mitt'
-
-const emitter = mitt()
-
-// listen to an event
-emitter.on('foo', e => console.log('foo', e) )
-
-// listen to all events
-emitter.on('*', (type, e) => console.log(type, e) )
-
-// fire an event
-emitter.emit('foo', { a: 'b' })
-
-// working with handler references:
-function onFoo() {}
-
-emitter.on('foo', onFoo)   // listen
-emitter.off('foo', onFoo)  // unlisten
-```
-
-**Event hub factory**
-
-We have created a factory that you can use to instantiate a new mitt-based event hub.
 This makes it easier to migrate existing event hubs to the new recommended approach, or
 to create new ones.