Idk about disabling the eggs (not sure this is possible, since it's a baked-in part of the creature), but since you're running simple spawners, you can use that to spawn it in, tie it to a simple spawners nest, and place the nest somewhere inaccessible to players (under the mesh, inside a redwood, etc.) This will make the egg untakeable by players, and allow the wyvern to roam free (provided you set the spawner governing it to global spawn).