fix: stabilize iOS launch and remove SceneDelegate dependency

whatsapp_app/ios/Runner/AppDelegate.swift

@@ -2,19 +2,13 @@ import Flutter
 import UIKit
 
 @main
-@objc class AppDelegate: FlutterAppDelegate, FlutterImplicitEngineDelegate {
+@objc class AppDelegate: FlutterAppDelegate {
   override func application(
     _ application: UIApplication,
     didFinishLaunchingWithOptions launchOptions: [UIApplication.LaunchOptionsKey: Any]?
   ) -> Bool {
-    if self.window == nil {
-      self.window = UIWindow(frame: UIScreen.main.bounds)
-      self.window?.rootViewController = UIViewController()
-    }
-    return super.application(application, didFinishLaunchingWithOptions: launchOptions)
+    let result = super.application(application, didFinishLaunchingWithOptions: launchOptions)
+    GeneratedPluginRegistrant.register(with: self)
+    return result
   }
-
-  func didInitializeImplicitFlutterEngine(_ engineBridge: FlutterImplicitEngineBridge) {
-    GeneratedPluginRegistrant.register(with: engineBridge.pluginRegistry)
-  }
-}
+}