Deprecate net/GeoIP, and expire it at the end of the month

Note that only the legacy format is deprecated. The GeoIP2 databases
are alive and well.

I completely missed that GeoIP has been deprecated for the last year,
and it expired upstream last week. Maxmind no longer provides the
legacy database, rendering this port useless.

Users must switch to GeoIP2 immediately. OPTIONS changes and
instructions will be coming in the next few days.

See https://support.maxmind.com/geolite-legacy-discontinuation-notice/

Although it won't be purged from the quarterly branch, it probably
makes sense to MFH this deprecation notice.

PR: 234715
Reported by: rigoletto
MFH: 2019Q1