Fix incorrect import in DynamicClassFixture

Author: hazzik

src/NHibernate.Test/EntityModeTest/Map/Basic/DynamicClassFixture.cs

@@ -1,9 +1,9 @@
-using System.Collections;
+using System;
+using System.Collections;
 using System.Collections.Generic;
 using System.Dynamic;
 using System.Linq.Dynamic.Core;
 using System.Linq;
-using Antlr.Runtime.Misc;
 using NUnit.Framework;
 using NHibernate.Criterion;