As of SERVER-75096, when the config server transitions to dedicated mode, it drops its drained sharded collections locally so it can later be added back without users directly dropping those collections on the config server first. The drop is in the first transitionToDedicatedConfigServer ran after all chunks and databases have been moved away. There may be pending range deletions though, so secondary reads may still be running or stale routers may target those collections with available read concern and expect to at least read orphans. For the same probabilistic guarantees as for normal migrations, we should only locally drop the collections after waiting for all pending range deletions to complete.