When user write blocking is enabled on a shardsvr, the associated critical section document has blockNewUserShardedDDL set to true. If now we convert this shardsvr back to replSet (which is a use case we account for), the replSet is hitting this invariant on startup due to seeing blockNewUserShardedDDL=true. Since it is not actually a problem that blockNewUserShardedDDL is true on a replSet (it is just ignored), we should remove this invariant.