Remove this from infra/README.md

> [!NOTE]
> Our staging to production migration script has been moved [here](<https://github.com/tahminator/codebloom/tree/main/.github/scripts/copy-prod-db/index.ts#L28>).

We run a SQL script after copying prod db to staging db to clean up the data:

https://github.com/tahminator/codebloom/blob/main/.github/scripts/copy-prod-db/index.ts#L82-L141

This script should be moved to infra/clean-stg-db.SQL and that TS file should then load that SQL file as a string and pass it into the shell command instead.

This will require a docs update inside of infra/README.md