MPT-26022 remove CODEOWNERS (#436)

🤖 AI-generated PR — Please review carefully.

## What
- Remove `.github/CODEOWNERS` so GitHub no longer requests
`@softwareone-platform/sirius` as reviewer automatically on every PR. PR
activity is now announced in Microsoft Teams.
- Branch protection on `main` does not require code owner reviews, so
merging is not affected.

Jira: [MPT-26022](https://softwareone.atlassian.net/browse/MPT-26022)


[MPT-26022]:
https://softwareone.atlassian.net/browse/MPT-26022?atlOrigin=eyJpIjoiNWRkNTljNzYxNjVmNDY3MDlhMDU5Y2ZhYzA5YTRkZjUiLCJwIjoiZ2l0aHViLWNvbS1KU1cifQ

<!-- This is an auto-generated comment: release notes by coderabbit.ai
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Closes [MPT-26022](https://softwareone.atlassian.net/browse/MPT-26022)

- Remove `.github/CODEOWNERS` to stop automatic review requests to
`@softwareone-platform/sirius`.

<!-- end of auto-generated comment: release notes by coderabbit.ai -->

Author: svazquezco