Have you tried just editing the 'user' role and removing the capability?
In the Manager, go into Access Controls, choose Roles, and look under Selected Capabilities. You should see a capability called 'get_typeahead' -- remove it and Save.
Alternately, edit local/authorize.conf and add:
[role_user]
get_typeahead = disabled
You might have to do that on more than one role, but for most people it will just be inherited from the default user role.
