cluster: refactor empty for in round_robin_handle.js

Author: gengjiawen

lib/internal/cluster/round_robin_handle.js

@@ -79,8 +79,10 @@ RoundRobinHandle.prototype.remove = function(worker) {
   if (this.all.size !== 0)
     return false;
 
-  for (var handle; handle = this.handles.shift(); handle.close())
-    ;
+  for (const handle of this.handles) {
+    handle.close();
+  }
+  this.handles = [];
 
   this.handle.close();
   this.handle = null;