PeriodicBalancerSettingsRefresher is currently unused because it was added as part of the intern autosplit project that didn't get finished over the summer.

It has two problems
1) It is instantiated incorrectly. It registers a shutdown task during sharding initialization, which can cause a crash if we're already in shutdown mode. The correct way to instantiate it it during single threaded start up of the server, where shutdown tasks can be safely registered, and then sharding initialization can simply start up the service.
2) Furthermore it is hitting an invariant in BF-6736, the solution for which is outlined in SERVER-31537

We're just going to remove PeriodicBalancerSettingsRefresher for now, because we don't need it and it is causing problems.