More precicely, there are no OT passages giving a general command to kill. God told specific people to kill specific foes for specific reasons. As such, these passages are perfectly useful today. They show how angry God was about those particular sins (infanticide, ritual sex abuse, occult practices, et al.)
The passages aren't useful unless God, today, gives a similar command. In Islam, the old passages still apply as a general instruction to kill the infidels.