transition from deprecated `map_dfr()` in `autoplot()` internals

[simonpcouch]

The internals of autoplot() for racing functions uses map_dfr(), a deprecated function from purrr:

https://github.com/tidymodels/finetune/blob/5e9d49ea935f0fc83f256fdf1c499b48d9b7401c/R/plot_race.R#L30

We should likely use map() and list_rbind() instead. https://github.com/tidymodels/recipes/pull/1204 is a good example of another PR that does the same.