This commit effectively reverts fix T45702 done in 067fe2719a.
Reasoning:
- Blender Internal is being replaced with Eevee, and will be removed entirely
rather soon.
- All render engines are planned to have own depsgraph, so such threading
conflicts should no longer be an issue.
- We don't want to spend time on porting workarounds for EOL things to a new
design. Less code -- faster the work :)
- If such notifications will end up needed for some other cases, we would
need to re-implement this a more proper depsgraph tagging/flushing and make
it to work with all copy-on-write datablocks and everything.
db2a603f6e