Removing the Conversation Tab is being reviewed by the feature team.
For deleting chat messages, please following progress here: https://microsoftteams.uservoice.com/forums/555103/suggestions/33535006.
An error occurred while saving the commentAnonymous commented
It is hard to believe there is no option to discard/delete a chat once it is concluded. Chat is very cluttered with misc/useless chats such as "Lunch at the diner in 10". All of that makes for a most user unfriendly experience.