Fix Retention, ObjectLock, LegalHold struct namespaces correctly. (#8909)

Reverts #8903 to allow structs to be unmarshalled 
even if the namespace is missing.

pkg/event/config_test.go

@@ -433,7 +433,7 @@ func TestConfigUnmarshalXML(t *testing.T) {
 	`)
 
 	dataCase3 := []byte(`
-	<NotificationConfiguration  xmlns="http://s3.amazonaws.com/doc/2006-03-01/">
+	<NotificationConfiguration>
 	   <QueueConfiguration>
 	      <Id>1</Id>
 	      <Filter></Filter>