Yahoo Placefinder service appears to have EOL'ed

Preamble/Meta

I couldn't decide between Priority Minor and Important. I think it's minor because the easy workaround is to switch to using Google's geocoder. I think it's important because it looks bad that we offer a geocoding provider that silently fails. Ultimately, I opted for the less dire-sounding priority.

Problem

The Yahoo Placefinder service that CiviCRM appears to support has reached end of life (EOL).

Evidence:

• Dumping the XML returned by the service in CRM_Utils_Geocode_Yahoo shows a message:

  geo.placefinder table is no longer supported

• Documentation for the service – at least I think this is the right doc; a lot of Yahoo services are similarly named – is preceded by this message:

  As announced in our Blog post, the Placefinder and Placemaker services are planned to be replaced on November 17th 2012 by the new BOSS Geo service. Please use our simple step by step tutorial to learn to migrate. We continue to offer a rate limited YQL table for Placefinder and Placemaker for non-commercial use. The free REST api's will no longer be actively supported."

• Our code references a domain query.yahooapis.com for the service; the doc for the new BOSS Geo implementation of the PlaceFinder service references yboss.yahooapis.com.
• CRM-18117: Report that Yahoo geocoding stopped working in 4.7.
• StackExchange question which was resolved by switching geocoding providers.

Proposed Solution

• Remove CRM_Utils_Geocode_Yahoo from the codebase.
• Look for other references to this service that should be removed (e.g., whatever mechanism populates the dropdown that allows Yahoo to be selected as the geocoder).
• Possibly add an upgrade step to core to deselect Yahoo as the geocoding service or to select Google.
• Encourage folks interested in continuing to use Yahoo geocoding to do so via extension.
• User documentation should be updated to reflect that Yahoo geocoding is no longer provided by core.

I'm volunteering to do this, but I'd like my findings and approach validated before I begin.