Deprecate SuppressWarning.hh with #warning

[scpeters]

🎉 New feature

Closes #348

Summary

The gz/utilities/SuppressWarning.hh header file is redundant with gz/utils/SuppressWarning.hh, so deprecate it.

Test it

Checklist

• [X] Signed all commits for DCO
• [ ] Added tests
• [ ] Added example and/or tutorial
• [ ] 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

Note to maintainers: Remember to use Squash-Merge and edit the commit message to match the pull request summary while retaining Signed-off-by messages.

[mjcarroll]

@scpeters I think this is good to un-draft?

[scpeters]

@scpeters I think this is good to un-draft?

I was hoping to test it before un-drafting it, and I haven't done that yet. I'll try updating one of the examples

[scpeters]

I tested it, and the #pragma wasn't generating a warning, so I switched to #warning, which will either print a compiler warning or fail with a compiler error. Either way it will get attention