remove lightgbm support?

[simonpcouch]

lightgbm currently has a dedicated bundling method, but will not need one when support for serialization via saveRDS + readRDS in the dev R package version (implemented in microsoft/LightGBM#4685) hits CRAN. It may be worth removing the lightgbm support before our initial CRAN release so we don't need to work through a deprecation cycle for those bundlers.

Their release timeline here: microsoft/LightGBM#5153

Related to tidymodels/bonsai#44—thanks for the note, @jameslamb. :)

[juliasilge]

This sounds like a good plan; let's remove the lightGBM support before the initial CRAN release. 👍