Chat has been integrated into Thunderbird years ago and you have never been able to "remove" it. You could remove the button for it in the toolbar, but as V115 has an empty toolbar by default (other than upgraded profile which retain their old icons as set). I really do not understand the question.

If you are talking about the entry on the spaces toolbar, I am not aware of a method to remove that entry. But that was a change from the last version, not the latest.