去掉UINavigationBar底部线条
[[UINavigationBar appearance] setBackgroundImage:[UIImage new] forBarPosition:UIBarPositionAny barMetrics:UIBarMetricsDefault];
[[UINavigationBar appearance] setShadowImage:[UIImage new]];
// 或者
self.navigationBar.clipsToBounds = YES;
去掉UITabBar顶部线条
self.tabBar.shadowImage = [UIImage new];
self.tabBar.backgroundImage = [UIImage new];
// 或者
self.tabBar.clipsToBounds = YES;
