radselect: Replace 1998 copy of radkfile with a more current version

The previous copy of radkfile was the one that shipped with xjdic
version 23, way back in 1998.  This file has seen countless updates and
corrections since then (including no longer listing 二 as a 1-stroke
radical).

The version included here is dated from August 2020, fetched from
http://nihongo.monash.edu/kradinf.html.