coverage: Remove sonar coverage setup

[dbussink]

Looks like this never was really enabled properly and it's not working at the moment. We never run these jobs on branches and the badge for sonarcloud is broken as well.

Let's remove this for now. If we want coverage back, we need to redo it anyway and newer Go releases like Go 1.20 have better support for doing coverage anyway so we'd need to do it differently regardless.

Checklist

• "Backport to:" labels have been added if this change should be back-ported
• Tests were added or are not required
• Did the new or modified tests pass consistently locally and on the CI
• Documentation was added or is not required

[vitess-bot]

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