remove accidental project leakage in api/ package

[notnoop]

nomad /api package should be divested from rest of nomad, to ease go mod adoption; but looks like we accidentally relied on helper/uuid due to my bad advice in #6650 (comment) .

Removed the accidental complexity, and inlined function to avoid declaring yet another go mod dependency for tests alone.

For some context, go mod treats test dependencies just like regular dependencies; and if github.com/hashicorp/nomad is marked as a dependency, then api users may need to declaring dependency on all of nomad main project transitively, which causes sadness given main app isn't go mod friendly yet and the project dependencies are many and large.

[drewbailey]

Woops, thanks for catching/fixing this! Fix makes sense, glad we can check w/ linting

[github-actions]

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