fix: avoid O(n^2) algorithm in cleanUpGlobalClassValue #898

[tometzky]

Fixes:

• [JENKINS-75200] Quadratic algorithm in SecureGroovyScript.cleanUpGlobalClassValue - repeated remove from array #898

Instead of removing elements from toRemove array while traversing it, which forces rewrite of the whole array each time, create a separate array toRemoveReally with elements that need to be removed.

Testing done

We're running our Jenkins instance on a patched version since March 2025. The instance has more than 10k jobs, almost all created with Groovy code by Jenkins DSL plugin. There was a dramatic drop of Jenkins CPU usage when the plugin was updated with with this change. We rebased the change several times since.

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 demonstrate the feature works or the issue is fixed

This is a performance change — it is not clear how to create a test case that demonstrates the change in a reasonable time.