Complete TODO listed in SERVER-21456

There is a TODO in the codebase referencing a resolved ticket which is assigned to you.

Please follow this link to see the lines of code referencing this resolved ticket:
https://github.com/mongodb/mongo/search?q=SERVER-21456&type=Code

The next steps for this ticket are to either remove the outdated TODO or follow the steps in the TODO if it is correct. If the latter, please update the summary and description of this ticket to represent the work you're actually doing.