Reduce the number of `Imports`

[Bisaloo]

To keep it under the 20 packages limit enforced by CRAN (fix #434).

• a499cc09daddbff9bacb8c72c26a451075af7adc removes magrittr
• 1c4ede02a1e4761e3976971c6642dcfc16567f3b removes tibble
• 4032abd72fde4d729cad65c0decb7766de12dfc4 removes stringi
• e677c4e96d67bdb30fd62d74eb268d3ecc44fb63 removes withr. I can revert it if you don't agree. It's not super good practice in general to silently supply an extra arg (progress) to a function where ... are already forwarded. You run the risk of having a issue do f(progress = FALSE) and then get a warning about an argument being supplied multiple times. But, in this specific case, given that the function is exclusively used internally, I think it's okay.

I would like to remove tidyselect as well but I'm a little bit perplexed about the strange case of where(). It doesn't seem to be explicitly re-exported from dplyr but:

library(dplyr)
#> 
#> Attaching package: 'dplyr'
#> The following objects are masked from 'package:stats':
#> 
#>     filter, lag
#> The following objects are masked from 'package:base':
#> 
#>     intersect, setdiff, setequal, union

starwars %>% 
  summarise(across(where(is.character), ~ length(unique(.x))))
#> # A tibble: 1 × 8
#>    name hair_color skin_color eye_color   sex gender homeworld species
#>   <int>      <int>      <int>     <int> <int>  <int>     <int>   <int>
#> 1    87         13         31        15     5      3        49      38

^{Created on 2021-11-30 by the reprex package (v2.0.1.9000)}

It's probably some tidyeval magick but it also means that we will probably get a warning about where being a global variable if we try it in the package. Maybe the best course of action is to ask dplyr devs if they could explicitly re-export where(), as they do for all the other tidyselect functions(??)

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