[Discover] Remove discover:searchFieldsFromSource setting

[jughosta]

• Closes [Discover] Deprecate discover:searchFieldsFromSource Advanced Setting #196501

Summary

The PR removes discover:searchFieldsFromSource Advanced Setting and the associated code.
This breaking change is planned for v9.

The setting was marked as deprecated in v8.15 #185871

Checklist

• Documentation was added for features that require explanation or tutorials
• Unit or functional tests were updated or added to match the most common scenarios
• The PR description includes the appropriate Release Notes section, and the correct release_note:* label is applied per the guidelines

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Pinging @elastic/kibana-data-discovery (Team:DataDiscovery)

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Pinging @elastic/obs-ux-management-team (Team:obs-ux-management)

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🤖 GitHub comments

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Just comment with:

• /oblt-deploy : Deploy a Kibana instance using the Observability test environments.
• run docs-build : Re-trigger the docs validation. (use unformatted text in the comment!)

[nreese]

kibana-presentation changes LGTM
code review only

[TinaHeiligers]

Usage collection and telemetry schema changes LGTM.
We are still waiting for a final confirmation for the BC, hence not approving quite yet.

[TinaHeiligers]

The BC has approved the change.
Code-related changes w.r.t usage collection and telemetry LGTM

[akowalska622]

LGTM, what a massive cleanup!

[opauloh]

Cloud Security changes LGTM

[peteharverson]

ML changes for the data visualizer LGTM

[janmonschke]

THI changes lgtm

[elasticmachine]

💚 Build Succeeded

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• Commit: 3e75600
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Metrics [docs]

Public APIs missing comments

Total count of every public API that lacks a comment. Target amount is 0. Run node scripts/build_api_docs --plugin [yourplugin] --stats comments for more detailed information.

id	before	after	diff
@kbn/discover-utils	227	226	-1
@kbn/management-settings-ids	137	136	-1
@kbn/unified-data-table	109	108	-1
total			-3

Async chunks

Total size of all lazy-loaded chunks that will be downloaded as the user navigates the app

id	before	after	diff
cloudSecurityPosture	502.7KB	502.5KB	-200.0B
dataVisualizer	614.8KB	614.8KB	-40.0B
discover	785.8KB	784.6KB	-1.1KB
esqlDataGrid	153.8KB	153.7KB	-82.0B
securitySolution	14.6MB	14.6MB	-618.0B
slo	855.0KB	854.8KB	-185.0B
unifiedDocViewer	115.8KB	115.8KB	+14.0B
total			-2.2KB

Page load bundle

Size of the bundles that are downloaded on every page load. Target size is below 100kb

id	before	after	diff
discover	44.1KB	44.0KB	-70.0B
unifiedDocViewer	11.8KB	11.3KB	-464.0B
total			-534.0B

Unknown metric groups

API count

id	before	after	diff
@kbn/discover-utils	277	276	-1
@kbn/management-settings-ids	138	137	-1
@kbn/unified-data-table	186	184	-2
total			-4

History

• 💚 Build #257288 succeeded a9a4bd9
• 💚 Build #256900 succeeded ece2ddd
• 💚 Build #256610 succeeded c3639c9
• 💛 Build #256457 was flaky bdf7582
• 💔 Build #256386 failed f1dec08

cc @jughosta