removed add_dependencies_to_description()

[nevrome]

I believe we can retire add_dependencies_to_description() now. The attachment package provides some solid functions that solve the underlying problem in a nice way.

The only thing missing there is an integration of the paper.Rmd file (and everything else outside of /R, /vignettes and /tests). But these paths can be added manually.

This PR is part of the #75 initiative.

[benmarwick]

Thanks for this, I wasn't aware of the 'attachment' package until you mentioned it in this PR. I've had a look at the package and tested it a bit. My opinion is that our add_dependencies_to_description() is more convenient and suitable for the compendium context. Our function requires no arguments, we run it once and it looks everywhere and updates the DESCRIPTION. With 'attachment' we have to think a bit more and do something like attachment::att_amend_desc(dir.r = "analysis/") (which doesn't do the same as add_dependencies_to_description() for me). Am I using 'attachment' incorrectly?