Blender Git Loki

Depsgraph: Remove object-specific flag which was storing update tag

There were following issues:

- This was used in a similar way of DEG's ID update callback. No reason to have
yet-another-way of informing editors/engines about changes. Better to keep
regular update mechanism usable and fast for those needs.
- It wasn't granular at all, and granularity in flags is something what we
need to support anyway, even for existing ID update.
- There is no reason to have it per-object. Depsgraph operates on IDs.
- It wasn't clear when and who clears the flag, and was possible to run into
conflicts.