Fix Obsolete messages

also remove unwanted .nupkg

Octokit.Reactive/IObservableGitHubClient.cs

@@ -16,7 +16,7 @@
         IObservableReleasesClient Release { get; }
         IObservableSshKeysClient SshKey { get; }
         IObservableUsersClient User { get; }
-        [System.Obsolete("The Notifications API belongs under the Activities client")]
+        [System.Obsolete("Notifications are now available under the Activities client. This will be removed in a future update.")]
         IObservableNotificationsClient Notification { get; }
         IObservableGitDatabaseClient GitDatabase { get; }
         IObservableSearchClient Search { get; }

Octokit/IGitHubClient.cs

@@ -116,7 +116,7 @@
         /// <remarks>
         /// Refer to the API docmentation for more information: https://developer.github.com/v3/activity/notifications/
         /// </remarks>
-        [System.Obsolete("The Notifications API belongs under the Activities client")]
+        [System.Obsolete("Notifications are now available under the Activities client. This will be removed in a future update.")]
         INotificationsClient Notification { get; }
 
         /// <summary>