Fixing some warnings (#6250)

Co-authored-by: Paul Ritter <ritter.paul1@googlemail.com>

Content.Server/Power/EntitySystems/ExtensionCableSystem.cs

@@ -1,4 +1,4 @@
-using System;
+using System;
 using System.Collections.Generic;
 using System.Diagnostics.CodeAnalysis;
 using Content.Server.Power.Components;
@@ -11,7 +11,6 @@ namespace Content.Server.Power.EntitySystems
 {
     public sealed class ExtensionCableSystem : EntitySystem
     {
-        [Dependency] private readonly IEntityLookup _lookup = default!;
         [Dependency] private readonly IMapManager _mapManager = default!;
 
         public override void Initialize()