[8.19] (backport #8559) TestGetArtifactName: Add test case + cleanup unused fields

[mergify]

Following up to #7804, this PR cleans up unused fields and adds a test case to the TestGetArtifactName unit test introduced in that PR.

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This is an automatic backport of pull request #8559 done by Mergify.

[mergify]

Cherry-pick of 0260c45 has failed:

On branch mergify/bp/8.19/pr-8559
Your branch is up to date with 'origin/8.19'.

You are currently cherry-picking commit 0260c4549.
  (fix conflicts and run "git cherry-pick --continue")
  (use "git cherry-pick --skip" to skip this patch)
  (use "git cherry-pick --abort" to cancel the cherry-pick operation)

Unmerged paths:
  (use "git add/rm <file>..." as appropriate to mark resolution)
	deleted by us:   internal/pkg/agent/application/upgrade/artifact/artifact_test.go

no changes added to commit (use "git add" and/or "git commit -a")

To fix up this pull request, you can check it out locally. See documentation: https://docs.github.com/en/pull-requests/collaborating-with-pull-requests/reviewing-changes-in-pull-requests/checking-out-pull-requests-locally

[elasticmachine]

Pinging @elastic/elastic-agent-control-plane (Team:Elastic-Agent-Control-Plane)

[elastic-sonarqube]

Quality Gate passed

Issues
0 New issues
0 Fixed issues
0 Accepted issues

Measures
0 Security Hotspots
No data about Coverage
0.0% Duplication on New Code

See analysis details on SonarQube

[elasticmachine]

💚 Build Succeeded

• Buildkite Build
• Commit: bd141f1

cc @ycombinator