Refs #6162 check this does not fail the tests

plugins/CustomVariables/Archiver.php

@@ -213,6 +213,7 @@ class Archiver extends \Piwik\Plugin\Archiver
             ) {
                 unset($row[Metrics::INDEX_NB_UNIQ_VISITORS]);
                 unset($row[Metrics::INDEX_NB_VISITS]);
+                unset($row[Metrics::INDEX_NB_USERS]);
             }
         }
     }