lv_LV locale: Correct the time part of d_t_fmt (bug 25324)

Currently d_t_fmt formats time as "plkst. %H un %M".  A quick Google
search says that "plkst." means "o’clock" and "un" means "and".
Also this format does not display seconds.

CLDR does not mention anything like that.  We have no reason to use
anything different than "%H:%M:%S".