Don't underline room topic

This makes finding out that the room dialog exists slightly difficult, but it looks nicer.

We could look into another way to make it obvious that room icon, title, and description are clickable.

lib/widgets/room_appbar.dart

@@ -119,7 +119,6 @@ class RoomAppbar extends ConsumerWidget implements PreferredSizeWidget {
                     overflow: TextOverflow.ellipsis,
                     style: Theme.of(context).textTheme.labelMedium?.copyWith(
                       color: Theme.of(context).colorScheme.onSurfaceVariant,
-                      decoration: TextDecoration.underline,
                     ),
                   ),
               ],