Remove incorrect redirection header

[scpeters]

🦟 Bug fix

Fix for abi-checker CI job split out from #301

Summary

The abi-checker job is failing for pull requests targeting gz-msgs9 (see #301 (comment)). I believe it should be fixed by removing this outdated ignition/msgs/test_config.h redirection header file, but the abi-checker job won't pass until after this is merged to gz-msgs9. As such, I've split this change into a separate PR to be merged first, and then we can rerun CI for #301, at which point it should pass.

Checklist

• Signed all commits for DCO
• Added tests
• Updated documentation (as needed)
• Updated migration guide (as needed)
• Consider updating Python bindings (if the library has them)
• codecheck passed (See contributing)
• All tests passed (See test coverage)
• While waiting for a review on your PR, please help review another open pull request to support the maintainers

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