refactor: remove startup script support

[roleyfoley]

Description

Removes startup script setup from the executor.

Motivation and Context

This functionality is now handled in the engine and script stores allow for sourcing startup repos from git based locations and s3

How Has This Been Tested?

Tested locally

Types of changes

• [ ] Bug fix (non-breaking change which fixes an issue)
• [X] Refactor (non-breaking change which improves the structure or operation of the implementation)
• [ ] New feature (non-breaking change which adds functionality)
• [ ] Breaking change (fix or feature that would cause existing functionality to change)

Followup Actions

• [x] None

Checklist:

• [ ] My change requires a change to the documentation.
• [ ] I have updated the documentation accordingly.
• [ ] I have added tests to cover my changes.
• [ ] All new and existing tests passed.
• [X] None of the above.