Merge actors in partitioned world dirties level

We've noticed that when we use the merge actors batch option, the partitioned world will get dirtied after the operation.

This occurs in FMeshMergeUtilities::MergeComponentsToInstances:

			if(bActuallyMerge)
			{
				// Create our actors
				const FScopedTransaction Transaction(LOCTEXT("PlaceInstancedActors", "Place Instanced Actor(s)"));
				Level->Modify();

• Create new empty open world
• Save current level
• Add two cubes
• Merge actors through batch method
• Notice that the world is now dirtied