[DOCS] Update RDF release notes
[DOCS] Update RDF release notes

- remove note on TIterationHelper renaming (it's internal)
- small clarification about support of `rdfentry_`, `rdfslot_`
- add mention that parallel execution is now saner

olifre/root,root-mirror/root,karies/root,root-mirror/root,karies/root,olifre/root,karies/root,olifre/root,karies/root,root-mirror/root,karies/root,karies/root,root-mirror/root,olifre/root,olifre/root,olifre/root,root-mirror/root,olifre/root,karies/root,olifre/root,karies/root,karies/root,root-mirror/root,root-mirror/root,olifre/root,olifre/root,karies/root,root-mirror/root,root-mirror/root,karies/root,root-mirror/root,root-mirror/root,olifre/root