Did you make the mistake of connecting your Facebook contacts and your phone on the iPhone OS 6? Well after a bit of fiddling I figured out there is an easy fix.
Go to settings.
Scroll down and click on Facebook.
Scroll down to where it says allow these apps to use account. Slide contacts to no. It then takes all your Facebook contacts off your phone.
On a related note if you want to make all the Facebook birthdays unlink also, slide it to no.