docs: update a few more IRC references
Here's two more Freenode -> OFTC reference updates that I intentionally left out of !10917 (merged). This was for two reasons:
- @craftyguy hadn't migrated yet when I wrote the patches
- #freenode hadn't migrated yet
It seems like the only mentions left of freenode in the repo is about flake-reporting in the CI-scripts. I'll leave that stuff up to @robclark to migrate.