Fix internal links in transformation

- Remove legacy-data.sql and change tests to use data.sql (legacy-data.sql was moved from cnx-upgrade when to_html.py was moved to cnx-archive, but it is almost identical to data.sql, so removing it.)
- Use the correct version in internal links
- remove parent path part of resources link: make it a host-relative link

The last commit is from #172.

Effort points: 2