Get rid of DNS_GEOIP_DATABASE_INIT explicit initializer for geoip dbs

Instead of the explicit struct initializer with all member, rely on the fact
that static variables are explicitly initialized to 0 if not explicitly
initialized.

lib/dns/tests/geoip_test.c

@@ -38,7 +38,7 @@
 /* Use GeoIP2 databases from the 'geoip2' system test */
 #define TEST_GEOIP_DATA "../../../bin/tests/system/geoip2/data"
 
-static dns_geoip_databases_t geoip = DNS_GEOIP_DATABASE_INIT;
+static dns_geoip_databases_t geoip;
 
 static MMDB_s geoip_country, geoip_city, geoip_as, geoip_isp, geoip_domain;