(Reuters) - Kraft Heinz Co beat Wall Street expectations for quarterly profit on Thursday as the struggling packaged food company reined in costs in the face of slowing demand for some of its main brands.The company has faced a rough year as it booked billions of dollars in writedowns in the value of some of its well-known brands, including Oscar Mayer, forcing it to slash dividends and scrap its full-year forecast.Shares of the company, which owns the Velveeta cheese and Heinz ketchup brands,..