Remove unused using statement

Author: troydai

src/Microsoft.Framework.FileSystemGlobbing/Internal/MatcherContext.cs

@@ -3,7 +3,6 @@
 
 using System;
 using System.Collections.Generic;
-using System.IO;
 using System.Linq;
 using Microsoft.Framework.FileSystemGlobbing.Abstractions;
 using Microsoft.Framework.FileSystemGlobbing.Internal.PathSegments;