Fixes build

mcs/class/System.Web/System.Web.dll.sources

@@ -1200,5 +1200,4 @@ System.Web/WebROCollection.cs
 System.Web/WebSysDescriptionAttribute.cs
 System.Web/XmlSiteMapProvider.cs
 ../corlib/System.Collections.Concurrent/SplitOrderedList.cs
-../corlib/System.Collections.Concurrent/ObjectPool.cs