Delete test-utils/README.md

[dead-claudia]

Description

Motivation and Context

We don't expose this publicly anymore, so there's literally no justification for this file's existence. (It already wasn't actually kept up to date with any sort of changelog.)

How Has This Been Tested?

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 change

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 document.
• I have added tests to cover my changes.
• All new and existing tests passed.
• I have updated docs/changelog.md