[ai_assistant] remove import from kbn/test-suites-xpack (elastic#228650)

## Summary

I just spotted that elastic#228009 made
an import from deprecated `x-pack/test` helper.

It usually leads to circular dependencies issue, so I updated the import
to the same helper already in solution directory and removed duplicated
directory (it was temp solution to avoid circular deps when moving tests
around, sorry for confusion)

I moved a few oblt helpers directly to Search solution search_playground
test dir, but we probably need to decouple "platform" part of it and
move to `kbn/test-suites-xpack-platform`

---------

Co-authored-by: kibanamachine <[email protected]>
(cherry picked from commit 122cd9a)

# Conflicts:
#	x-pack/test/api_integration/deployment_agnostic/apis/observability/ai_assistant/utils/knowledge_base.ts
#	x-pack/test/tsconfig.json

Author: dmlemeshko

.github/CODEOWNERS

@@ -1926,7 +1926,6 @@ x-pack/test/functional/services/index.ts @elastic/appex-qa
 /x-pack/platform/test/serverless @elastic/appex-qa
 /x-pack/test/api_integration/deployment_agnostic @elastic/appex-qa
 /x-pack/platform/test/functional/services/ml/api.ts @elastic/appex-qa # temporarily due to SKA tests relocation
-/x-pack/test/api_integration/deployment_agnostic/apis/ @elastic/appex-qa # temporarily due to SKA tests relocation
 /x-pack/solutions/observability/test/functional/config.base.ts @elastic/appex-qa
 /x-pack/solutions/observability/test/functional/ftr_provider_context.d.ts @elastic/appex-qa
 /x-pack/solutions/observability/test/functional/page_objects/index.ts @elastic/appex-qa

x-pack/solutions/observability/test/api_integration_deployment_agnostic/apis/ai_assistant/complete/functions/retrieve_elastic_doc.spec.ts

@@ -10,12 +10,12 @@ import { ChatCompletionStreamParams } from 'openai/lib/ChatCompletionStream';
 import { ChatCompletionMessageParam } from 'openai/resources';
 import { last } from 'lodash';
 import { MessageAddEvent, MessageRole } from '@kbn/observability-ai-assistant-plugin/common';
-import { TINY_ELSER_INFERENCE_ID } from '@kbn/test-suites-xpack/api_integration/deployment_agnostic/apis/observability/ai_assistant/utils/model_and_inference';
 import { LlmProxy, createLlmProxy } from '../../utils/create_llm_proxy';
 import { chatComplete } from '../../utils/conversation';
 import type { DeploymentAgnosticFtrProviderContext } from '../../../../ftr_provider_context';
 import { installProductDoc, uninstallProductDoc } from '../../utils/product_doc_base';
 import {
+  TINY_ELSER_INFERENCE_ID,
   deployTinyElserAndSetupKb,
   teardownTinyElserModelAndInferenceEndpoint,
 } from '../../utils/model_and_inference';