Remove unused PowerManagement

It isn't up to the application to prevent the system from going to sleep

MediaBrowser.Model/System/IPowerManagement.cs

@@ -1,11 +0,0 @@
-using System;
-
-namespace MediaBrowser.Model.System
-{
-    public interface IPowerManagement
-    {
-        void PreventSystemStandby();
-        void AllowSystemStandby();
-        void ScheduleWake(DateTime wakeTimeUtc, string displayName);
-    }
-}