Remove ignored fallback option on GeoIP processor

[PeteGillinElastic]

This removes the option fallback_to_default_databases on the geoip ingest processor has been deprecated and ignored since 8.0.0.

[elasticsearchmachine]

Hi @PeteGillinElastic, I've created a changelog YAML for you. Note that since this PR is labelled >breaking, you need to update the changelog YAML to fill out the extended information sections.

[elasticsearchmachine]

Pinging @elastic/es-data-management (Team:Data Management)

[joegallo]

Do any uses of DEFAULT_DATABASES_DEPRECATION_MESSAGE remain after this change? If not, I think you should remove the variable definition, too.

[PeteGillinElastic]

Do any uses of DEFAULT_DATABASES_DEPRECATION_MESSAGE remain after this change? If not, I think you should remove the variable definition, too.

Good call, done.

[leemthompo]

@PeteGillinElastic is this PR relevant to the serverless changelog? [FYI this question is based on 9.0 breaking changes]

[PeteGillinElastic]

@PeteGillinElastic is this PR relevant to the serverless changelog? [FYI this question is based on 9.0 breaking changes]

I think this depends on the policy for the serverless changelog. This property was deprecated and ignored since 8.0.0, so nobody should have been using it in serverless. I don't know whether this should be mentioned or not.

[PeteGillinElastic]

Also, this change was made in November, before serverless GA.