Remove redundant hierarchies & remove two Goldbook defs

[dalito]

Thank you for opening a Pull Request! After submitting, please confirm:

• I have not copied concept definitions from sources with licenses incompatible with voc4cat's CC0 license (e.g., copyleft licenses like CC-BY-SA).
• I have cited sources that influenced my definitions (in Influenced by IRIs) or from which definitions were adapted (in Source Vocab IRI). Note: You may cite IUPAC Goldbook as an influence, but not copy its definitions verbatim due to its CC-BY-SA license.
• I have created a meaningful PR title and referenced any related issues.

---

• The PR removes 4 redundant hierarchy relations, see 🐞 Remove redundant hierarchies #231
• Adds new improved definitions for terms 7040/7041 where IUOAC Goldbook definitions had been copied verbatim which we prefer to avoid due to its CC-BY-SA licence (see new PR template note above). These were the only definitions affected as far as we know (please make an issue otherwise).

Closes #231