Remove references to GPL v2.0 license
    
    All FreeIPA original code should be licensed to GPL v3+ license,
    update the respective files:
    
    - daemons/ipa-slapi-plugins/ipa-dns/ipa_dns.c
    
    Remove GPL v2.0 license files from LDIFs or template to keep
    consistency.
    
    Reviewed-By: Simo Sorce <ssorce@redhat.com>