STYLE: removal of files from github repo (#601)

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[AB#45134](https://sqlclientdrivers.visualstudio.com/c6d89619-62de-46a0-8b46-70b92a84d85e/_workitems/edit/45134)

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### Summary   
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required. -->
This pull request removes the `OneBranchPipelines/github-ado-sync.yml`
file, which previously defined the entire pipeline for syncing the main
branch from the public GitHub repository to the internal Azure DevOps
repository. This pipeline automated daily synchronization and managed
divergent histories between the two repositories.

The most important change is:

Pipeline removal:

* Deleted the `OneBranchPipelines/github-ado-sync.yml` file, which
contained the full configuration for the GitHub-to-ADO sync pipeline,
including scheduling, branch sync logic, conflict handling, and
automated pull request creation in Azure DevOps.

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Author: subrata-ms