In previous versions, the PlanCache tracked the score associated with a cache entry for several historical executions of the cached plan. These scores were then surfaced via the planCacheListPlans comment, which was deprecated in 4.2 and removed in 4.4. The number of historical executions tracked was controlled by the internalQueryCacheFeedbacksStored setParameter.
Since this information is no longer surfaced by the replacement for planCacheListPlans (the $planCacheStats agg stage), the code for tracking this "feedback" information can be deleted. The internalQueryCacheFeedbacksStored setParameter can also be deleted.