Deprecate extra gd:structuredPostalAddress fields.

For the purposes of contact data, there are some postal
address columns that are unsupported, since they don't
directly contribute to a "mailing address" for a person.

http://code.google.com/apis/contacts/docs/3.0/reference.html#structuredPostalAddressRestrictions
http://code.google.com/apis/gdata/docs/2.0/elements.html#gdStructuredPostalAddress