[Room list] Use the items from Element instead of the duplicated Tchap ones

[Florian14]

The request is to remove the TchapRoomSummaryItem which is a copy of the RoomSummaryItem from Element with some changes. There are not too many differences between the items, so we can keep the one from Element. It will be better for us as we will inherit the Element changes during the rebase, it will just require resolving some conflicts but this should be not too difficult to maintain.