Apparently you are using an SSID, that has its VLAN setting set to "Virtual Controller Assigned".
If you change that VLAN settings, then you should not get IP from the internal DHCP server.
You can change the default DHCP server scope from 172.x to something else but you can not disable it.
However as explained above, you can stop using it on the SSID, by changing the VLAN settings.