[v11] Drop support for deprecated notification methods

[paulb777]

In conjunction with Auth (#13003) and GoogleUtilities v9, drop support for (void)application:(UIApplication *)application didReceiveRemoteNotification:(NSDictionary *)userInfo in favor of (void)application:(UIApplication *)application didReceiveRemoteNotification:(NSDictionary *)userInfo fetchCompletionHandler:`

The PR also fixes decoder warnings that show up running the unit tests.

Fix #11693

[google-oss-bot]

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[ncooke3]

nice to see a couple less deprecated blocks 👍

[DemetAkyolKapar]

When I remove didReceiveRemoteNotification, which method will be used instead?
I am using 10.24.0 version sdk and the didReceiveRemoteNotification method is not called, what can I do?
{"message":{"notification":{"title":"Test","body":"Feed"},"data":{"message":"Feed"},"apns":{"headers":{"apns-priority":"10"},"payload":{"aps":{"badge":1,"collapse_key":"FCM_Sender","content_available":true,"time_to_live":90,"sound":"default"}}},"token":"c........"}}

@paulb777 @pragatimodi