refactor to import core utilities

[cboettig]

Core codemeta.json elements from DESCRIPTION (and CITATION) can now be extracted with codemeta, https://cran.r-project.org/web/packages/codemeta/index.html (using stripped-down versions of the same functions from here). Now that this lightweight version is on CRAN, we should re-import that here rather than duplicate the code.

[maelle]

Can this be closed or is there more refactoring to do @cboettig?