We already implicitly require magic restore to restore a replica set node, since the replicaSetConfig parameter in the restore configuration is required. We should enforce that by requiring the --replSet parameter when --magicRestore is present. This will prevent the user from accidentally running the restore on a standalone node. While this is probably safe, there are subtle differences between the two, and we often check isReplSet. It makes it easier to reason about if we limit users to specifying --replSet.