tools: Cleanup more unused code

[dbussink]

This removes tools/statsd.go which seems entirely unused. It also removes a number of dependencies from tools/tools.go that we don't use anymore.

This is mainly around linting where we use golangci-lint now and not these separate ones anymore.

Found when working on #12987 where I audited all default mux usages.

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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