You can convert the AP into a standalone mode by factory defaulting the AP. There is no other way to get the ZD info wiped off the AP. Also if you connect the AP to a ZD managed AP, the AP will always connect to the ZD.
In case you do not want the AP to connect to the ZD on the network, you can SSH into the AP and execute the command : set director ip 184.108.40.206 220.127.116.11 and then reboot the AP, this will stop the AP from connecting to the controller on the network.
Hope this helps.