The `BVHCacheType bvh_cache_type` parameter defines specific
`BVHTrees` that cannot be customized.
So it doesn't make sense to pass this value to any
`*bvhtree_from_[...]_ex` function as the `BVHTrees` created in these
cases are custom and cannot be saved in the cache.
This also resulted in a nice cleanup in the code.
Differential Revision: https://developer.blender.org/D14479