bsdinstall TUI utility

Hello,


So far I replaced and adapted `dialog` with `bsddialog` in
bsdinstall/scripts.
<https://wiki.freebsd.org/RoadmapFromDialogToBSDDialog>


Currently, I am addressing the last 4 scripts: auto, bootconfig, keymap,
and wlanconfig. These scripts use also the $DIALOG variable and some
"if" to handle Xdialog(1).
For example 'auto' uses $DIALOG, $USE_XDIALOG, and `dialog`.

* $DIALOG: I seem bsdinstall(8) uses only dialog(1) as TUI utility.
* I seem bsdconfig(8) does not "call" these 4 scripts, so, probably,
   Xdialog(1) is not used in this context (that is `bsdconfig -X`).


Is there any objection to delete $DIALOG/LGPL-dialog/Xdialog to
provide only the support for bsddialog(1) in bsdinstall(8)?

I would prefer this solution because I can avoid: to handle some
dialog/Xdialog/bsddialog command line difference and to hook some
bsdconfig function built on dialog(1) incompatible with bsddialog(1)
(for example autosizing, implemented in bsddialog(3) already).


Please note these considerations are only for bsdinstall, bsdconfig is
unchanged.


Best regards,
Alfonso