South Dakota Gov. Kristi Noem scrambled Friday to justify her admission to gunning down her family’s dog and goat in a gravel pit — by saying she’d also killed horses. The Republican governor recounted the killings in her forthcoming memoir, “No Going Back: The Truth on What’s Wrong with Politics and How We Move America Forward,” saying the 14-month-old pup had an “aggressive personality” and proved herself “untrainable.” She recounted how she led the wirehair pointer to a gravel pit and fatally shot it before dragging a “nasty and mean” male goat to meet the same fate. Want more breaking poli…