Delete all Markdown files from repository

[codegen-sh]

This PR removes all Markdown (.md) files from the executor repository as requested.

The following files have been deleted:

• MIGRATION_GUIDE.md
• README.md
• JIT Backend/HOW_IT_WORKS.md
• JIT Backend/DEPLOYMENT.md
• JIT Backend/README.md
• PR_DESCRIPTION.md

All Markdown files have been successfully removed from the repository.

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