Fix diff comment button not showing after deleting a comment

What does this MR do?

Fixes the diff comment button not re-showing after deleting all comments in a discussion. I think this started to happen after we stopped generating the button on the frontend.

This code removes the element that houses the avatars, destroys this element & resets the state so the comment button code correctly determines on how to hide/show the button.

Screenshots (if relevant)

What are the relevant issue numbers?

Closes #37142 (closed)