chore: remove release-comment workflow

[maxisbey]

Removes the release-comment workflow that was added in #1750.

Motivation and Context

The workflow failed on its first run (https://github.com/modelcontextprotocol/python-sdk/actions/runs/20068484009) because it comments on both PRs and linked issues, requiring issues: write permission. After review, the workflow isn't needed - contributors can watch releases or subscribe to the repo for notifications.

How Has This Been Tested?

N/A - removes a workflow.

Breaking Changes

None.

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)
• Documentation update

Checklist

• I have read the MCP Documentation
• My code follows the repository's style guidelines
• New and existing tests pass locally
• I have added appropriate error handling
• I have added or updated documentation as needed

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