Remove deprecated sort mode from geo_sort

[nik9000]

This removes the deprecated sort_mode key from _geo_distance sorting. It's been deprecated since 5.0.

[elasticsearchmachine]

Pinging @elastic/es-analytical-engine (Team:Analytics)

[elasticsearchmachine]

Hi @nik9000, 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.

[craigtaverner]

Changelog needs updating

[craigtaverner]

Suggested change

	summary: Remove deprecated sort mode from `geo_sort`
	summary: Remove deprecated `sort_mode` from sort by `_geo_distance`

[craigtaverner]

Suggested change

	title: Remove deprecated sort mode from `geo_sort`
	title: Remove deprecated `sort_mode` from sort by `_geo_distance`

[craigtaverner]

This section appears to be a template, and should be replaced.

[craigtaverner]

I updated the changlog, but while area: Geo was allowed, breaking.area: Geo was not, so I changed that to breaking.area: Search.

[iverase]

I wonder if we still need to support Rest API compatibility here, so if the user adds to the call compatible-with=8 should still work?

[nik9000]

Having talked with a few folks we're not going to remove this. It's just not worth disrupting the tiny percentage of users that might use this. I'm going to close this and add a comment saying such so folks don't try this again.

[craigtaverner]

Interesting, if we cannot remove anything as low impact as this (no behavioural change, only syntax change) deprecated as far back as 5.0, is it really possible to remove anything at all?