Remove the old user status (reaction/emoji)

[antobinary]

In BigBlueButton 2.7 we introduced Reactions https://docs.bigbluebutton.org/2.7/new-features/#reactions-bar
We kept the old user status behind configuration flag even though that made things fairly complex.
In BBB 3.0 we are refactoring and cleaning things up. We would rather not have to re-implement the old user status (especially since everyone we're aware of has switched to Reactions). Therefore we're dropping it.

https://github.com/bigbluebutton/bigbluebutton/blob/v2.7.x-release/bigbluebutton-html5/private/config/settings.yml#L158-L159
https://github.com/bigbluebutton/bigbluebutton/blob/v2.7.x-release/bigbluebutton-html5/private/config/settings.yml#L624-L639

TODO:

• drop the configuration in settings.yml
• drop the client code
• drop the core code
• check if anything is needed in recording processing (do we need to retire an event? If so, document it)
• document that we're removing it

Related: #20261