Remove httpclient dependency

[strangelookingnerd]

Remove direct dependency to apache-httpcomponents-client-4-api at it is only used for HttpStatus.SC_NOT_FOUND in a test.

Testing done

mvn clean verify

Submitter checklist

• Make sure you are opening from a topic/feature/bugfix branch (right side) and not your main branch!
• Ensure that the pull request title represents the desired changelog entry
• Please describe what you did
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• Ensure you have provided tests - that demonstrates feature works or fixes the issue

[strangelookingnerd]

@jenkinsci/gitlab-branch-source-plugin-developers Kindly requesting a review.

[MarkEWaite]

Change makes sense to me. The plugin does not directly depend on the apache-httpcomponents-client-4-api but it does depend on the gitlab-api plugin and the gitlab-api plugin depends on apache-httpcomponents-client-4-api.