Zombie nautiluses can spawn on peaceful

Zombie nautiluses can spawn on peaceful, this is not consistent with the other undead mounts.

Steps to reproduce the issue:

• As seen in MC-304797, be on peaceful, load the the seed -8790581265353131111, use: /tp -9591 63 8825 then teleport to the nearest zombie nautilus, it still spawned despite being on peaceful

• Another example is using monster spawners, the spawner works on peaceful.

Expected result:

• They should not spawn on peaceful at all for consistency with other undead mounts.

Actual result:

• They spawn.