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

• 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

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[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