tzsetup: adapt for libbsddialog 0.0.1

libbsdialog 0.0.1 provides:

• bsddialog_conf.auto_minwidth:
• menurows is variable with autosize (properly defines max menurows)

Then tzsetup can use BSDDIALOG_AUTOSIZE keeping the dialog behavior:
min 24 cols, max 16 menurows

Differential revision: https://reviews.freebsd.org/D33397