Converting the bucket notification test to typed clients left the
framework notification plumbing it was the last consumer of unused.
Remove the NotificationOperation client, TopicClient.CreateHTTPServer,
BucketClient.CreateObcNotification and CheckBucketNotificationSetonRGW
(and the now-dead UpdateObcNotification helpers), and the
GetBucketNotification and GetOBCNotification manifest builders.
Signed-off-by: Joshua Hoblitt <josh@hoblitt.com>