Update backup.py

Remove unused func `check_vm_backup_metadata`
diff --git a/staffeln/conductor/backup.py b/staffeln/conductor/backup.py
index c393866..519b81c 100755
--- a/staffeln/conductor/backup.py
+++ b/staffeln/conductor/backup.py
@@ -23,12 +23,6 @@
 )
 
 
-def check_vm_backup_metadata(metadata):
-    if not CONF.conductor.backup_metadata_key in metadata:
-        return True
-    return metadata[CONF.conductor.backup_metadata_key].lower() in ["true"]
-
-
 class Backup(object):
     """Implmentations of the queue with the sql."""