Removed clean checkout workaround

[ricellis]

Checklist

• [x] Tick to sign-off your agreement to the Developer Certificate of Origin (DCO) 1.1
• [x] Added tests for code changes or test/build only changes
• [x] Updated the change log file (CHANGES.md|CHANGELOG.md) or test/build only changes
• [x] Completed the PR template below:

Description

Remove the Jenkinsfile clean checkout workaround.

Fixes #506

Approach

The referenced Jenkins issue was resolved and the option to clean before checkout is now specified in the multi-branch configuration rather than in the Jenkinsfile.

Schema & API Changes

• "No change"

Security and Privacy

• "No change"

Testing

• N/A build or packaging only changes

Monitoring and Logging

• "No change"