Migrate from lazyeval to rlang

As part of [Resolve namespace conflicts among packages attached by library(inventory)](https://github.com/BAAQMD/inventory/issues/19) we would like to remove all occurences of `lazyeval` in the codebase and replace them with rlang. According to RStudio: _lazyeval has been superseded by rlang. We're working on better communicating these changes to the user with deprecation messages using lifecycle._

`funtools` has one usage of `lazyeval`:
```
pmean <- function (..., na.rm = TRUE) {
dots <- lazyeval::lazy_dots(...)
args <- lazyeval::lazy_eval(dots)
f <- function (...) base::mean(c(...), na.rm = na.rm)
purrr::pmap_dbl(args, f)
}
```
We should find a way to convert this code to use rlang, so that we can remove the package completely from our setup.

Search the codebase and package setup for `lazyeval`, then inspect the `pmean` entry point shown in the issue. Compare the existing lazy argument handling with the relevant rlang approach and check any package tests or checks. Done means the usage is migrated and no `lazyeval` dependency or occurrence remains.

Written by the indexing model from the issue text.