Revert the XEngine memleak patch, it causes premature GC.

This matches behavior seen with an earlier attempt to do this, apparently
the sponsor mechanism does't work in Mono

OpenSim/Region/ScriptEngine/Interfaces/IScript.cs

@@ -41,7 +41,5 @@ namespace OpenSim.Region.ScriptEngine.Shared.ScriptBase
         Dictionary<string,Object> GetVars();
         void SetVars(Dictionary<string,Object> vars);
         void ResetVars();
-
-        void Close();
     }
 }