GitLab

* [R-package] remove unused code and comments

* put check back

* other typos

* [R-package] improvements to lgb.convert() functions (fixes #2678, #2681)

* more stuff

* update docs

* remove lgb.convert()

* put internal functions back

* update index

* [R-package] deprecate lgb.prepare() and lgb.prepare2()

* linting

* renaming

* updated docs

* linting

* Apply suggestions from code review
Co-authored-by: Nikita Titov <nekit94-08@mail.ru>

* one more comment fix

* remove comment about int being dangerous

* empty commit
Co-authored-by: Nikita Titov <nekit94-08@mail.ru>