Remove duplicated setTimeout in error callback

https://api.jquery.com/jQuery.ajax/
According to JQuery doc, `complete` will be called whether the ajax
request succeeds or fails. As a result, `_refreshClusterStatus` will
generates two new scheduled calls if the ajax request gets an error
response (one by `error` and one by `complete`).
If `_refreshClusterStatus` keeps getting error responses (e.g. token
has expired), it will generate a huge number of requests (doubles every
30s)

src/ui/app/jsx/cluster-list.jsx

@@ -64,8 +64,6 @@ const Cluster = CreateReactClass({
           },
           error: function(data) {
             console.error(this.component.props.name + " failed.");
-            this.component.setState({clusterStatuses: setTimeout(this.component._refreshClusterStatus, 30000)});
-
           }
       });
   },