Tiles traverser: do not check for visibility in canTraverse.

[Avnerus]

Hi!
Yet another fix for tile traversal. Bug was noticed while traveling in Google's 3D Tiles.
The canTraverse function should not check for visibility in the traversal process, as shown in the CesiumJS code. Probably there are cases where a parent in the traversal process is not visible, but the child tile is.
Here is how it looked before the fix:

And here is how it looks after:

Possibly, this functionality existed previously via the ignoreVisibility argument. Now I removed both optional arguments from canTraverse since they are not used.

If approved, would it be possible to merge this PR to the current stable branch?

Thank you,
/Avner

[ibgreen]

Thanks. I see that there was a flag already. From a quick look I don't see that flag documented or referenced elsewhere, so should be fine to just remove it.

[Avnerus]

Thank you! Do you think we can merge this to the stable branch?
@felixpalmer @belom88

[ibgreen]

Thank you! Do you think we can merge this to the stable branch? @felixpalmer @belom88

To prepare for a possible appropval, you could make a cherry-pick PR against 4.2-release branch.

[Avnerus]

Thank you.
I opened the cherry-picked PR at #3039.
It seems to be failing the test but with a reason not related to the commit.