NORTH READING, MASS. — Executive "dress codes" are fading away at United States corporations.A survey commissioned by footwear manufacturer, Converse Inc., of North Reading, Mass., found that some 55 percent of the companies responding approve of casual or "less formal" executive styles of dress. By a more than 8-to-1 margin, companies also said executive dress habits are becoming less traditional. Only 22 percent of the companies have formal dress codes. The biggest shift to "less formal" business clothing has been among women executives. Instead of traditional business suits, more are wearing shorter skirts and dresses, and flats or open-toed shoes.