Remove cffconvert action and mentions to create a zenodo.json

[abelsiqueira]

A Zenodo entry is created automatically from CITATION.cff, so there's no need to create it anymore. Therefore, the cffconvert action should be removed. There are also mentions to creating a zenodo.json in README.dev.md.

[bouweandela]

A Zenodo entry is created automatically from CITATION.cff, so there's no need to create it anymore.

Some Zenodo features are not supported by the CITATION.cff file format, such as listing grants: https://developers.zenodo.org/#github. In that case you still need a separate .zenodo.json file.

[abelsiqueira]

We should still remove the action, though, since it will fail in those cases as well - if I understood the action correctly. For the mentions to zenodo.json, we can add a notice like "If enabled, Zenodo will create an entry automatically from your CITATION.cff file. If you want to overwrite that information, for instance , to specify information not supported by the CFF format, you should create a .zenodo.json file separately".

[sjvrijn]

Completed, see e.g. 4c25c480