[stable/zed] Drop extra log_config_append for Nova (#1371)

This is an automated cherry-pick of #1359
/assign mnaser
diff --git a/roles/nova/vars/main.yml b/roles/nova/vars/main.yml
index b7a93c2..6434640 100644
--- a/roles/nova/vars/main.yml
+++ b/roles/nova/vars/main.yml
@@ -106,7 +106,6 @@
         auth_schemes: vencrypt,none
     nova_ironic:
       DEFAULT:
-        log_config_append: null
         force_config_drive: true
   manifests:
     deployment_consoleauth: false