Cannot delete device /dev/pps0

I have been playing with gpsd and ntpd. I was trying to figure out if my usb gps device had a pulse per second output, it did not. I used ldattach 18 /dev/ttyACM0 (or a very similar device which was my usb gps) to create /dev/pps0. Now, despite the usb gps being unplugged and rebooting, /dev/pps0 remains. I have not got any rules for it in /ete/udev/rules.d etc nor anything in rc.local which creates it. I can't see how to get rid of it.

I want rid of it as it may be confusing things now I have a usb gps with working PPS that I want to connect.

Just doing this for fun, because I can.