roles/ipaclient/defaults/main.yml: Remove default values for some vars

This is needed to be able to use defined and undefined checks.

roles/ipaclient/defaults/main.yml

 ---
 # defaults file for ipaclient
 
-ipaclient_domain:
-ipaclient_realm:
-
-ipaclient_principal:
-ipaclient_password:
-ipaclient_keytab:
-ipaclient_otp:
 ipaclient_force_join: no
-ipaclient_kinit_attempts:
 ipaclient_ntp: no
 ipaclient_mkhomedir: no
-ipaclient_extraargs: [ ]
\ No newline at end of file