Deprecate metro code

Author: oschwald

CHANGELOG.md

@@ -4,6 +4,8 @@
 
 * Ruby 3.0+ is now required. If you're using Ruby 2.5, 2.6, or 2.7, please
   use version 1.2.0 of this gem.
+* Deprecated `metro_code` on `MaxMind::GeoIP2::Record::Location`. The code
+  values are no longer being maintained.
 
 ## 1.2.0 (2023-12-04)
 

lib/maxmind/geoip2/record/location.rb

@@ -46,11 +46,11 @@ def longitude
           get('longitude')
         end
 
-        # The metro code of the location if the location is in the US. MaxMind
-        # returns the same metro codes as the Google AdWords API. See
-        # https://developers.google.com/adwords/api/docs/appendix/cities-DMAregions.
+        # The metro code is a no-longer-maintained code for targeting
+        # advertisements in Google.
         #
         # @return [Integer, nil]
+        # @deprecated Code values are no longer maintained.
         def metro_code
           get('metro_code')
         end