[AI] Moving navmesh and navbounds to a sublevel results in a level nearly twice the size expected

Using World Composition, moving the Navmesh and NavmeshBounds from the persistent level to a sub-level results in the size of the navmesh sub-level being roughly twice the size of the decreased size of the persistent level. Running build paths after moving keeps the file sizes roughly the same. 

I have been able to get the file size for the sub-level to be what one would expect (navmesh sub-level is slightly larger than the amount the persistent level decreased). To do this, I would:

1. Load both the persistent and sub-level
2. Hide/toggle the visibility of the persistent world in the Levels tab
3. Build paths to get the navmesh to disappear as no geometry is in the scene
4. Save the sub-level
5. Re-enable the persistent level
6. Build paths again
7. Save both levels.
8. Check the size of the levels on disk. It should be nearly the size the persistent level decreased when moving the navmesh and navbounds.

1. Create a new level called World_0
2. Add a large plane and navmeshbounds volume
3. Build Paths
4. Create a new level as a sub-level to World_0 that is called World_0_Navmesh
5. Save new sub-level
6. Note the size on disk of both World_0 and World_0_Navmesh
7. Move the NavmeshBounds volume and Recast Navmesh actor to World_0_Navmesh
8. Build Paths
9. Save both levels
10. Node the size on disk of both World_0 and World_0_Navmesh

Expected Result: World_0 has decreased in size and World_0_Navmesh has increased nearly the same amount that World_0 has decreased.

Actual Result: World_0 decreases and World_0_Navmesh increases to be roughly twice the size of the decrease for World_0.