McDonald’s has opened at the site of the old Arby’s at 11710 Rockville Pike — but good luck finding a place to sit down. In a new concept being tested by the fast-food chain, all orders at this location must be placed at the drive-through, online or via a kiosk in the lobby. There are only five seats inside — two at a table, three at a bar. If you don’t snag one of them, you might have to eat in your car. Meanwhile, the Pike’s previous McDonald’s location near Nicholson Lane will soon reopen as Dave’s Hot Chicken.