nit: remove unused method from OneSignalExtensionBadgeHandler header

* currentCachedBadgeValue is only used within the OneSignalExtensionBadgeHandler class, no need to expose on header.

Author: nan-li

iOS_SDK/OneSignalSDK/OneSignalExtension/OneSignalExtensionBadgeHandler.h

@@ -31,5 +31,4 @@
 
 @interface OneSignalExtensionBadgeHandler : NSObject
 + (void)handleBadgeCountWithNotificationRequest:(UNNotificationRequest *)request withNotification:(OSNotification *)notification withMutableNotificationContent:(UNMutableNotificationContent *)replacementContent;
-+ (NSInteger)currentCachedBadgeValue;
 @end