WEST PALM BEACH, Fla. — The shortened spring training has taken at least one victim on the Mets rotation. Taijuan Walker’s knee pain has resurfaced in the past week, leading up to his disappointing Tuesday start in the Mets’ 14-0 loss to the Nationals. He underwent knee surgery in January, and had been progressing nicely up until the final week of Mets camp. On Tuesday, Walker allowed six runs, including two home runs, across just 1 1/3 innings against the Nats in his final tune-up of spring training. He threw a perfect first inning, then allowed six hits in the second inning. Somewhat alarmin…