With the recent powerdns upgrade, the GeoIP backend uses a new config
format, see zones-file.yml.jinja2.

zz.countries.nexedi.dk.rbldnsd (which maps IPs to countries) is replaced
by GeoLite2-Country.mmdb(1) (which maps IPs to countries & continents).

Note: zz.countries.nexedi.dk.rbldnsd is not deleted (yet?); it is parsed
to keep information about China and its IP ranges grouped by ISP.

cdn.conf.in (which maps RR(s) to countries) is dropped; it is replaced
by an equivalent mapping done inside zones-file.yml.jinja2.

Also, EDNS Client Subnet extension is enabled.

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(1): Added in previous commit.