Remove regex for retention_metadata_key

Current regex is not correct
diff --git a/staffeln/conf/conductor.py b/staffeln/conf/conductor.py
index ab2a61a..8a2d409 100755
--- a/staffeln/conf/conductor.py
+++ b/staffeln/conf/conductor.py
@@ -57,10 +57,6 @@
     ),
     cfg.StrOpt(
         "retention_metadata_key",
-        regex=(
-            r"((?P<years>\d+?)y)?((?P<months>\d+?)mon)?((?P<weeks>\d+?)w)?"
-            r"((?P<days>\d+?)d)?((?P<hours>\d+?)h)?((?P<minutes>\d+?)min)?((?P<seconds>\d+?)s)?"
-        ),
         help=_(
             "The key string of metadata the VM, which use as backup retention period."
         ),