Don't use the created timestamp for package lag calculation (#568)

Progress on NuGet/NuGetGallery#6506

Author: joelverhagen

src/Monitoring.RebootSearchInstance/FeedClient.cs

@@ -25,7 +25,6 @@ public class FeedClient : IFeedClient
 
         private static readonly IEnumerable<string> TimeStampProperties = new string[]
         {
-            "Created",
             "LastEdited",
         };