The unsetSharding command removes a connection's associated shardVersions.

As part of dropCollection, the config server sends unsetSharding to all shards over the TaskExecutor/NetworkInterface networking stack, but all commands run through the TaskExecutor that need versioning information attach that information to the command being run directly, rather than setting it on the connection via the setShardVersion command. So, this unsetSharding command is a no-op, and can be removed.