remove dependencies

[idavydov]

Hi,

This is to remove several library dependencies, including:

• magrittr (native pipe instead + R4.1 is a requirement now)
• glue (stringr::str_glue() is used instead)
• checkmate for R6 checking is replaced with R6::is.R6() + inherits()
• forcats (using as.factor() or factor() instead)
• tidyselect (using re-exports in dplyr namespace instead)

we could remove in the future (but with a lot of work):

• stringr
• purrr

I'd say it's not worth it now.

@banfai could you please take a look?

fyi @klmr