[cli/dev] rely on commander for deduping argv (elastic#14181)

In eb31780 I started combining custom argv with the process's argv, and naively used union to combine the lists. This breaks cli arguments that are supposed to be repeated and isn't necessary since commander handles parsing the argv and deduping/merging based on config.

src/cli/cluster/worker.js

@@ -39,10 +39,9 @@ export default class Worker extends EventEmitter {
     this.clusterBinder = new BinderFor(cluster);
     this.processBinder = new BinderFor(process);
 
-    const argv = _.union(baseArgv, opts.argv || []);
     this.env = {
       kbnWorkerType: this.type,
-      kbnWorkerArgv: JSON.stringify(argv)
+      kbnWorkerArgv: JSON.stringify(baseArgv.concat(opts.argv || []))
     };
   }