Martin Slumbers could not have witnessed greater theater than his first British Open in charge of the R&A, the record-setting duel between Henrik Stenson and Phil Mickelson at Royal Troon. “I walked around quite a bit and it felt sort of empty,” Slumbers, 64, said in a telephone interview this week as he winds down nearly a decade as CEO. The final Open for Slumbers, who retires at the end of the year, also was at Royal Troon this summer when Xander Schauffele battled through rain and wind on Saturday and emerged with his second major of the year.