[ios] Remove unused ivars from MainControler

ios/chrome/app/main_controller.mm

Index: ios/chrome/app/main_controller.mm
diff --git a/ios/chrome/app/main_controller.mm b/ios/chrome/app/main_controller.mm
index 833e747a19cef643c9fba5444a30775d6d4bcce0..f4cd02e7d93b17300eaad14f77e2599a8e31fdef 100644
--- a/ios/chrome/app/main_controller.mm
+++ b/ios/chrome/app/main_controller.mm
@@ -268,14 +268,6 @@ enum class StackViewDismissalMode { NONE, NORMAL, INCOGNITO };
   base::scoped_nsobject<SigninInteractionController>
       _signinInteractionController;
 
-  // The number of memory warnings that have been received in this
-  // foreground session.
-  int _foregroundMemoryWarningCount;
-
-  // The time at which to reset the OOM crash flag in the user defaults. This
-  // is used to handle receiving multiple memory warnings in short succession.
-  CFAbsoluteTime _outOfMemoryResetTime;
-
   // YES while animating the dismissal of stack view.
   BOOL _dismissingStackView;