[CHORE] Leftover X Pack references

[ashwin-pc]

Description

There are still some x-pack references in the code that need to be removed.

• https://github.com/opensearch-project/OpenSearch-Dashboards/blob/main/src/plugins/data/README.md?plain=1#L114
• https://github.com/opensearch-project/OpenSearch-Dashboards/blob/main/packages/osd-pm/src/utils/validate_dependencies.ts#L178
• https://github.com/opensearch-project/OpenSearch-Dashboards/blob/main/src/core/server/saved_objects/migrations/core/index_migrator.test.ts#L145
• https://github.com/opensearch-project/OpenSearch-Dashboards/blob/main/src/core/server/saved_objects/migrations/core/index_migrator.test.ts#L168
• https://github.com/opensearch-project/OpenSearch-Dashboards/blob/main/src/core/server/saved_objects/migrations/core/opensearch_index.ts#L314
• https://github.com/opensearch-project/OpenSearch-Dashboards/blob/main/src/dev/notice/cli.js#L83
• https://github.com/opensearch-project/OpenSearch-Dashboards/blob/main/src/plugins/apm_oss/server/tutorial/instructions/apm_server_instructions.ts#L39

Credits: @AMoo-Miki

To Reproduce
Steps to reproduce the behavior:

1. Go to the link
2. See the X Pack reference

Expected behavior
We should not have any X Pack references in the code

OpenSearch Version
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Dashboards Version
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Plugins

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Screenshots

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Host/Environment (please complete the following information):

• OS: [e.g. iOS]
• Browser and version [e.g. 22]

Additional context

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[vimalMK]

Can I do the clean up unless anyone else is already working on it?

[kavilla]

@vimalMK feel free to work on it! Let us know if you need any help on it!

[vimalMK]

@kavilla Thank you! I have a question before PR. In the last link(file)

https://github.com/opensearch-project/OpenSearch-Dashboards/blob/main/src/plugins/apm_oss/server/tutorial/instructions/apm_server_instructions.ts#L39

Shall I remove the whole default message and keep it empty or do you want something like " If you're using an secured version of Elastic Stack, you must specify credentials in the apm-server.yml config". ?