Revert "last(1): unbreak for 8-bit locales"

This reverts commits 8e67c427b5 (unbreak for 8-bit locales), 0ca58ca151
(correction after r351413), and f424ec1b80 (fix style after r351459).

A simpler fix can be done by using the h modifier for strings that are
encoded with the current locale.

Reviewed by: eugen, philip
Differential Revision: https://reviews.freebsd.org/D32437