(Corrects headline and paragraph 2 to say profit warning rather than second warning as November statement was a downgrade) By James Davey and Suban Abdulla LONDON (Reuters) -Britain’s Burberry blamed a worsening slowdown in demand for luxury goods for its second downgrade in three months, and warned of a tough challenge ahead as it launches a strategy to move upmarket, in a blow to its shares. Burberry’s profit warning is a major setback to CEO Jonathan Akeroyd’s turnaround plan as he tries to lift the brand under the creative guidance of designer Daniel Lee, whose first collection was introdu…