Remove dead store to set the keyPairProvider

[MarkEWaite]

Remove dead store to set the keyPairProvider

No need to set the keyPairProvider to a default value then immediately set it to a different value.

Storing once should be enough.

Detect as the only production use of SimpleGeneratorHostKeyProvider in the Jenkins code base while investigating for jenkinsci/jenkins#7623

• 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

[daniel-beck]

Unused import remains.