Fix #704, allow delete without device_auth

* This typically comes up when using a deployment.yml generated from
   some inventory source, the device disappears and can then no
   longer be deleted since netdisco-delete unnecessarily insists on
   needing a valid device_auth

lib/App/Netdisco/Worker/Runner.pm

@@ -51,7 +51,7 @@ sub run {
 
     # per-device action but no device creds available
     return $job->add_status( Status->defer('deferred job with no device creds') )
-      if 0 == scalar @newuserconf;
+      if 0 == scalar @newuserconf && $job->action ne "delete";
   }
 
   # back up and restore device_auth