Prefer Geo::IP over GeoIP2

GeoIP2 doesn't support ASN data yet, so...

- try to load Geo::IP first
- if GeoIP2 is loaded instead, warn about lack of ASN data
previously, if both GeoIPCity and GeoLiteCity database files existed, we would load the GeoIPCity DB, then immediately replace it with GeoLiteCity.  This eliminates that redundancy