Two-time and reigning WBA heavyweight champion Nikolai Valuev isn’t letting constant trash- talking by 3-time world cruiserweight champion David Haye get into his head as he makes final preparations for Saturday’s “David vs. Goliath” world title fight being broadcast in North America live on Pay-Per-View from Nuremberg, Germany. Valuev (50-1, 34 KOs), from St. Petersburg,…