SERVER-44139 adds the RecoveryUnit as an argument to KVEngine::dropIdent in order to accommodate scenarios (e.g., transactions) that cannot depend on the same OperationContext being available in onCommit/onRollback handlers. Mobile is the only storage engine that depends on opCtx for reasons other than obtaining the corresponding RecoveryUnit, so the OperationContext argument should be removed from dropIdent once the mobile storage engine is removed.