After an index build is completed (committed/aborted) the document representing the active index build state in config.system.indexBuilds is removed by the IndexBuildsCoordinator. This was done in
SERVER-47635. In certain abort situations, if a secondary votes for commit readiness as the primary is in removing the document, we may end up with an orphaned document in this system collection. It would be desirable, for better resource management, to periodically clean up the replicated config.system.indexBuilds collection on the primary.