Use Jenkins colour palette for Prism instead of tomorrow

[janfaracik]

Following jenkinsci/prism-api-plugin#161 it's no longer necessary for Jenkins themes to declare what theme Prism should use. This is due to the default Prism theme now using the default Jenkins colour palette for its colours, meaning that as long as themes override them Prism will pick them up automatically.

Before

After

Testing done

• Prism looks as expected

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2. Ensure that the pull request title represents the desired changelog entry
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4. Link to relevant issues in GitHub or Jira
5. Link to relevant pull requests, esp. upstream and downstream changes
6. Ensure you have provided tests - that demonstrates feature works or fixes the issue

[timja]

Thanks!