Web UI tests: Get rid of *_cert_path and *_csr_path config variables
    
    Web UI tests now don't require additional configuration to test certificates.
    Self-signed certificates and CSR are generated on fly.
    Next variables from ~/.ipa/ui_test.conf for now are deprecated:
    - arbitrary_cert_path
    - service_csr_path
    - user_csr_path
    
    Ticket: https://pagure.io/freeipa/issue/7843
    Reviewed-By: Sergey Orlov <sorlov@redhat.com>
    Reviewed-By: Florence Blanc-Renaud <flo@redhat.com>