Fix double-tagging in .SingleXXX() query

Author: SergeiPavlov

Orm/Xtensive.Orm/Orm/Internals/Prefetch/EntityGroupTask.cs

@@ -136,11 +136,6 @@ private QueryTask CreateQueryTask(List<Tuple> currentKeySet)
       Func<object, object> generator = CreateRecordSet;
       var session = manager.Owner.Session;
       Provider = (CompilableProvider) session.StorageNode.InternalQueryCache.GetOrAdd(key, generator);
-      if (session.Tags != null) {
-        foreach (var tag in session.Tags) {
-          Provider = new TagProvider(Provider, tag);
-        }
-      }
       var executableProvider = session.Compile(Provider);
       return new QueryTask(executableProvider, session.GetLifetimeToken(), parameterContext);
     }