(iOS) Revert "co-existence with cordova-plugin-local-notification on …

…iOS"

Upon testing, this plugin does not work with `cordova-plugin-local-notification` present in the same project even with this code in place.
Therefore removing it should stop the crashes occurring in #385.
And the conflict between the 2 plugins will need to be addressed separately under #230.

This reverts commit 4e9a0f4:

> co-existence with cordova-plugin-local-notification on iOS

> Local notifications on iOS via cordova-plugin-local-notification are working again.
>Click-callback for remote notifications not working right now.

>Details:
>UNUserNotificationCenter accepts a single delegate that handles the display of notifications. cordova-plugin-firebase now stores a reference to the existing delegate if any and proxies the delegate-calls (cordova-plugin-local-notification is >already doing that in the other direction when applicable).

src/ios/AppDelegate+FirebasePlugin.m

@@ -13,7 +13,6 @@ @interface AppDelegate () <UNUserNotificationCenterDelegate, FIRMessagingDelegat
 @end
 
 #define kApplicationInBackgroundKey @"applicationInBackground"
-#define kDelegateKey @"delegate"
 
 @implementation AppDelegate (FirebasePlugin)
 
@@ -28,14 +27,6 @@ + (AppDelegate*) instance {
 static bool authStateChangeListenerInitialized = false;
 static bool shouldEstablishDirectChannel = false;
 
-- (void)setDelegate:(id)delegate {
- objc_setAssociatedObject(self, kDelegateKey, delegate, OBJC_ASSOCIATION_RETAIN_NONATOMIC);
-}
-
-- (id)delegate {
- return objc_getAssociatedObject(self, kDelegateKey);
-}
-
 + (void)load {
  Method original = class_getInstanceMethod(self, @selector(application:didFinishLaunchingWithOptions:));
  Method swizzled = class_getInstanceMethod(self, @selector(application:swizzledDidFinishLaunchingWithOptions:));
@@ -108,10 +99,6 @@ - (BOOL)application:(UIApplication *)application swizzledDidFinishLaunchingWithO
  [FirebasePlugin.firebasePlugin handlePluginExceptionWithoutContext:exception];
  }
  }];
-
- // Set UNUserNotificationCenter delegate
- self.delegate = [UNUserNotificationCenter currentNotificationCenter].delegate;
- [UNUserNotificationCenter currentNotificationCenter].delegate = self;
 
  // Set NSNotificationCenter observer
  [[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(tokenRefreshNotification:)
@@ -394,14 +381,6 @@ - (void)userNotificationCenter:(UNUserNotificationCenter *)center
  withCompletionHandler:(void (^)(UNNotificationPresentationOptions options))completionHandler {
 
  @try{
- if(center == nil){
- center = [UNUserNotificationCenter currentNotificationCenter];
- }
- if(center != nil){
- [self.delegate userNotificationCenter:center
- willPresentNotification:notification
- withCompletionHandler:completionHandler];
- }
 
  if (![notification.request.trigger isKindOfClass:UNPushNotificationTrigger.class] && ![notification.request.trigger isKindOfClass:UNTimeIntervalNotificationTrigger.class]){
  [FirebasePlugin.firebasePlugin _logError:@"willPresentNotification: aborting as not a supported UNNotificationTrigger"];
@@ -470,14 +449,6 @@ - (void) userNotificationCenter:(UNUserNotificationCenter *)center
  withCompletionHandler:(void (^)(void))completionHandler
 {
  @try{
- if(center == nil){
- center = [UNUserNotificationCenter currentNotificationCenter];
- }
- if(center != nil){
- [self.delegate userNotificationCenter:center
- didReceiveNotificationResponse:response
- withCompletionHandler:completionHandler];
- }
 
  if (![response.notification.request.trigger isKindOfClass:UNPushNotificationTrigger.class] && ![response.notification.request.trigger isKindOfClass:UNTimeIntervalNotificationTrigger.class]){
  [FirebasePlugin.firebasePlugin _logMessage:@"didReceiveNotificationResponse: aborting as not a supported UNNotificationTrigger"];