Make sure mapping cache is cleared when deleting a user

This avoids phantom remnants staying after user deletion

Signed-off-by: Côme Chilliet <come.chilliet@nextcloud.com>

apps/user_ldap/lib/Mapping/AbstractMapping.php

@@ -380,6 +380,11 @@ abstract class AbstractMapping {
 			DELETE FROM `' . $this->getTableName() . '`
 			WHERE `owncloud_name` = ?');
 
+		$dn = array_search($name, $this->cache);
+		if ($dn !== false) {
+			unset($this->cache[$dn]);
+		}
+
 		return $this->modify($statement, [$name]);
 	}