api: Do not use sqs for ListenBucketNotification. (#3023)

Add more tests. Fixes #3024

cmd/bucket-notification-datatypes.go

@@ -160,17 +160,6 @@ type NotificationEvent struct {
 	S3                eventMeta         `json:"s3"`
 }
 
-// Represents the minio topic type and account id's.
-type arnTopic struct {
-	Type      string
-	AccountID string
-}
-
-// Stringer for constructing AWS ARN compatible string.
-func (m arnTopic) String() string {
-	return minioTopic + serverConfig.GetRegion() + ":" + m.AccountID + ":" + m.Type
-}
-
 // Represents the minio sqs type and account id's.
 type arnSQS struct {
 	Type      string