Remove unsupported font-smoothing class

[bipoza]

🗒️ Description

This change removes the unsupported font-smoothing class. The webkit and moz versions are valid, but font-smoothing is not standard. In the case of the Chrome engine, it takes the webkit classes.

More info: https://caniuse.com/mdn-css_properties_font-smooth

🎥 Artifacts

W3C validator

✔️ Checklist

• Changelog entry
  in the readme.txt file.
• Code is covered by NEW wpunit or integration tests.
• Code is covered by EXISTING wpunit or integration tests.
• Are all the required tests passing?
• Automated code review comments are addressed.
• Have you added Artifacts?
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