关于隐藏或删除顶部的导航条 的问题

代码成功运行，但是在页面顶部多出来一个导航条，我想隐藏起来或者删除。

ClsMainPageAppDelegate.m 
#import "ClsMainPageAppDelegate.h"
#import "ClsTermsandConditionViewController.h"
- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions
{
    UIStoryboard *storyboard = [UIStoryboard storyboardWithName:@"MainStoryboard" bundle:nil];
    ClsTermsandConditionViewController *ivc = [storyboard instantiateViewControllerWithIdentifier:@"termsandConditionControl"];
    UINavigationController *navigationController=[[UINavigationController alloc] initWithRootViewController:ivc];
    self.window.rootViewController=nil;
    self.window.rootViewController = navigationController;
    [self.window makeKeyAndVisible];
}