remove map_dfr - fixes posit-dev/connectapi#422

[AntLP]

Intent

As described in the issue, some functions had a dependency on dplyr through the use of purrr::map_df and purrr::map_dfr.

Fixes #422

Approach

Replaced the calls to purrr::map_df and purrr::map_dfr with a combination of purrr::map and purrr::list_rbind, which removes the dependency on dplyr.

I did not remove the purrr::map_dfr usages in the tests, dplyr is therefore still required to run the tests.

Checklist

• Does this change update NEWS.md (referencing the connected issue if necessary)?
• Does this change need documentation? Have you run devtools::document()?