SERVER-76855 introduces RoutingCollator, which provides the machinery to allow mongos to ignore a collator for untracked collections (so as to prevent attaching the simple collator to a command). This is needed to allow commands routed to unsharded collections to discovery the collection default collation when the reach the shard which owns them. Once we branch for 8.0, however, we will know the collection default collection for unsharded collections on mongos as they will now be tracked collections. As such, this code will no longer be necessary and can be deleted when master is on version 8.1.