Remove unused usings

Author: Robert Holt

Engine/CommandInfoCache.cs

@@ -1,10 +1,7 @@
 using System;
 using System.Collections.Concurrent;
-using System.Collections.Generic;
-using System.Linq;
 using System.Management.Automation;
-using System.Threading;
-using System.Threading.Tasks;
+using System.Linq;
 
 namespace Microsoft.Windows.PowerShell.ScriptAnalyzer
 {