[Obs AI] Remove the knowledge base tool

[viduni94]

Closes https://github.com/elastic/obs-ai-assistant-team/issues/408

Summary

This PR removes the search_knowledge_base tool from the Observability Agent. We will reintroduce it later.

Checklist

• The PR description includes the appropriate Release Notes section, and the correct release_note:* label is applied per the guidelines
• Review the backport guidelines and apply applicable backport:* labels.

[elasticmachine]

Pinging @elastic/obs-ai-team (Team:obs-ai)

[elasticmachine]

💛 Build succeeded, but was flaky

• Buildkite Build
• Commit: 09c28a3

Failed CI Steps

• Jest Tests #4

Test Failures

• [job] [logs] Jest Tests #4 / Both modes Primary menu More menu should have persistent popover on hover out after the trigger was clicked
• [job] [logs] Jest Tests #4 / Both modes Primary menu Primary menu item limit should display a "More" menu item with a submenu when more than 12 exist
• [job] [logs] Jest Tests #4 / xy style settings Axis settings should pass in endzone visibility setter and current sate for time chart
• [job] [logs] Jest Tests #4 / xy style settings Axis settings should pass in extent information

Metrics [docs]

Unknown metric groups

References to deprecated APIs

id	before	after	diff
observabilityAgent	2	0	-2

History

• 💔 Build #364372 failed b87d390
• 💚 Build #363893 succeeded 1e8cdfb

cc @viduni94