Reduce `DupliObject::persistent_id` from 16 to 8 items
Reduce `DupliObject::persistent_id` from 16 to 8 items

For historical reasons, `DupliObject::persistent_id` was of size
`2*MAX_DUPLI_RECUR`. These reasons are now gone, and the persistent ID
always gets exactly one array element for every dupli-recursion.

Differential Revision: https://developer.blender.org/D8222

Reviewed by: brecht

tangent-opensource/coreBlackbird,tangent-opensource/coreBlackbird,tangent-opensource/coreBlackbird