/**
  * listDelete
  * Delete a user from the list.
  *
  * @param $email_address the email address to delete
  *
  */
 public static function listDelete($email_address)
 {
     global $CFG;
     $listid = $CFG->block_mailchimp_listid;
     //First obtain the memberID for the email address.
     $memberid = helper::getMemberID($listid, $email_address);
     $method = "lists/" . $listid . "/members/" . $memberid;
     if (!($api = new \DrewM\MailChimp\MailChimp($CFG->block_mailchimp_apicode))) {
         debugging("ERROR: Unable to create mailchimp wrapper object \\DrewM\\MailChimp\\MailChimp.");
         return false;
     }
     $result = $api->delete($method);
     if ($result !== false) {
         debugging("ERROR: Unable to remove user " . $email_address . " from mailchimp, method: " . $method . "\nResult: " . print_r($result) . "\n");
         return false;
     }
     return true;
 }