docs: Replace duplicate Maintainer list

[nschonni]

Description

Keep the README.md as the central spot for any list memberships.

Motivation and Context

Currently the Maintainers list is in both the README and GOVERNANCE, which could lead to sync issues if one is updated.
I was going to add myself to the Maintainers (since I've had that Team permission for some time), but thought this cleanup made sense to do first.

Testing Details

Example Output(if appropriate)

Types of changes

• Documentation
• Version change (Update, remove or add more Node.js versions)
• Variant change (Update, remove or add more variants, or versions of variants)
• 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)
• Other (none of the above)

Checklist

• My code follows the code style of this project.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have read the CONTRIBUTING.md document.
• All new and existing tests passed.

[MikeMcC399]

This PR makes no changes in any roles and it consolidates lists into one place for better maintenance. Since it has already been approved by an official "maintainer", I'm merging it in.