Remove double 'kph' metric unit

[wschoot]

Context

It seems the unit "kph" was specified twice. I've corrected this

Contributor Checklist

• [x] Review Contribution Guidelines
• [x] Agree to the terms of Developer Certificate of Origin.
• [x] Make sure all contributed code can be distributed under the terms of the GNU Licence
• [x] Check "Allow edit from maintainers" option in pull request so that additional changes can be pushed by maintainers if required.
• [x] Unit tests created/updated (under tests) to verify logic, and approval tests for UI Widgets
• [x] Update Examples - Under build-scripts/examples, and regenerate examples docs if required ( make doc-examples )
• [x] Ensure that tests pass locally - this can be tricky for approval tests with maps or text though.
• [x] Check that pre-release tests work ( make test-distribution )

[time4tea]

Thanks!