games: Move out non (6) utilities from /usr/games/.

games: Move out non (6) utilities from /usr/games/.

The strfile(8) and unstr(8) are pretty generic on their own and do not belong
in /usr/games/ (with all NO_GAMES stuff). All (6) utilities are still in games.

 * Move stfile(8) and unstr(8) to usr.bin/.
 * Move out strfile from btools and convert it to hostprog (like nvi).
 * Compile strfile.nx only if NO_SHARE is not set.

While there, apply 3rd to usr.bin/vi too (somehow skipped it in bf31779ebd).