Remove Enable Exits On Suspend flags on iOS

ios/chrome/app/UIApplication+ExitsOnSuspend.h

-// Copyright 2012 The Chromium Authors. All rights reserved.
-// Use of this source code is governed by a BSD-style license that can be
-// found in the LICENSE file.
-
-#ifndef IOS_CHROME_APP_UIAPPLICATION_EXITSONSUSPEND_H_
-#define IOS_CHROME_APP_UIAPPLICATION_EXITSONSUSPEND_H_
-
-#if !defined(NDEBUG)
-
-#import <UIKit/UIKit.h>
-
-// Key in the UserDefaults for toggling exit on suspend.
-extern NSString* const kExitsOnSuspend;
-
-// WARNING: This is intended for non AppStore builds, since it's not allowed to
-// quit an app programmatically. Internally we call exit(0).
-@interface UIApplication (ExitsOnSuspend)
-
-// When the app goes in background, terminate the app when all background tasks
-// have finished. Use this in -applicationDidEnterBackground:.
-- (void)cr_terminateWhenDoneWithBackgroundTasks;
-
-// Cancel termination. Use this in -applicationWillEnterForeground:.
-- (void)cr_cancelTermination;
-
-@end
-
-#endif  // !defined(NDEBUG)
-
-#endif  // IOS_CHROME_APP_UIAPPLICATION_EXITSONSUSPEND_H_