I agree w/ Scott. Generally, there isn't a lintel even used with arches anyway as they are pretty good at supporting themselves. That said, the flatter they are, the less effective they are at that job. But in this case, the brick load above is minimal. If there's been no movement in 30 years, I don't expect much if anything now. Barring some outward force acting on it that's not present now, of course.