By Sean Walsh England manager Gareth Southgate decided against calling up Manchester United youngster Kobbie Mainoo for this month’s friendlies against Brazil and Belgium, despite his fine performances this season. The Three Lions have one last mid-season window ahead of this summer’s European Championships in Germany, though Southgate neglected to call upon one of the best players at one of the Premier League’s biggest clubs. Instead, Mainoo was called into the England Under-21 setup for the first time. When the unpopular Jordan Henderson is still making squads, it’s understandable that fans …