Tarik Skubal is headed for arthroscopic surgery to remove loose bodies from his left elbow after his arm locked up. Detroit doesn’t yet have a firm timetable for his return, though the procedure has historically cost pitchers roughly two to three months. Skubal was scratched from his scheduled start against the Red Sox after a flare-up, five days after an earlier scare against the Braves.   That is a Tigers problem first. It’s a brutal one, too. Skubal is one of the best pitchers on the planet, the kind of ace who changes how a team feels every fifth day. Before the injury, he had a 2.70 ERA with 45 strikeouts over 43 1/3 innings, and the Tigers were trying to build their season around the kind of certainty he usually provides.   But for the Mariners, this should still feel familiar in a different way. Because every time we start talking ourselves into the idea that Seattle has too many starters, baseball tends to clear its throat.…