Clean-up sample

Author: josesimoes

Samples/ListJLinkDevicesApp/Program.cs

@@ -3,12 +3,8 @@
 // See LICENSE file in the project root for full license information.
 ////
 
-using System;
-using System.Collections.Generic;
-using System.Linq;
-using System.Text;
-using System.Threading.Tasks;
 using nanoFramework.Tools.FirmwareFlasher;
+using System;
 
 namespace ListJLinkDevicesApp
 {