rework static files server

MareSynchronosServer/MareSynchronosStaticFilesServer/FileStatisticsService.cs

@@ -1,11 +1,5 @@
 using MareSynchronosShared.Metrics;
-using Microsoft.Extensions.Hosting;
-using Microsoft.Extensions.Logging;
-using System;
 using System.Collections.Concurrent;
-using System.Linq;
-using System.Threading;
-using System.Threading.Tasks;
 
 namespace MareSynchronosStaticFilesServer;