For those looking for OBJC solution, to be added in App Delegate didFinishLaunchingWithOptions method:
[[UINavigationBar appearance] setBackgroundImage:[UIImage new] forBarMetrics:UIBarMetricsDefault];
[UINavigationBar appearance].shadowImage = [UIImage new];
[UINavigationBar appearance].backgroundColor = [UIColor clearColor];
[UINavigationBar appearance].translucent = YES;