Remove duplicate GHSA-4fr2 reference

[cookesan]

Removes the malformed duplicate WhiteSource reference from GHSA-4fr2-j4g9-mppf while leaving the clean CVE-2020-28271 reference intact.

Audit refresh, July 8, 2026:

• Confirmed the advisory still retains the clean WhiteSource URL, NVD URL, and upstream fix commit reference.
• Confirmed the GHSA and NVD records for CVE-2020-28271 still resolve.
• Local checks passed: one advisory JSON file changed in the PR diff, JSON parses, git diff --check passes, and the worktree is clean.