Right-hander Taijuan Walker, the Mariners’ top prospect, will be shut down from all throwing for two weeks after an examination Wednesday revealed what club officials characterized as a “right shoulder impingement.” The announcement came one day after Walker was scratched from a rehab start at Triple-A Tacoma because of stiffness in his arm. “What we’re going to do,” general manager Jack Zduriencik said, “is back him off for about two weeks and take care of the area. Then, he’ll begin throwing, and we’ll have to build him back up.” The Mariners previously halted Walker from all throwing for one week in early March after an examination revealed bursitis. But he had been pain-free once he resumed his throwing program and was on pace to rejoin the rotation in the near future.