HTMLUnit 3.x

[timja]

Part of jenkinsci/jenkins-test-harness#568

Testing done

Tested in stapler and jenkins-test-harness

Upgrade guide:
https://www.htmlunit.org/migration.html

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
• Link to relevant issues in GitHub or Jira
• Link to relevant pull requests, esp. upstream and downstream changes
• Ensure you have provided tests - that demonstrates feature works or fixes the issue

[timja]

shaded version was not being used anywhere as far as I can tell so let's not pretend we're doing it anymore

not sure if we fully want to remove the shade plugin or if that will cause issues