Duplicate case in TableViewDelegate.responds(to:)

There are two identical cases in `TableViewDelegate.responds(to:)`, both checking `TableViewDelegate.tableView(_:sectionForSectionIndexTitle:at:)` ([L486:L489](https://github.com/vhesener/Closures/blob/master/Xcode/Closures/Source/UITableView.swift#L486:L489)).