test(plugin-security): delete the platform-admin seeding suites here, directly before the code they pin (#15204 stage 6b-2, T1)

Moved from the 6b-2a PR: no pin of a behaviour 6b-2 deletes leaves main before
6b-2. Their double-contract ledger entries go with them.

Co-Authored-By: Claude <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_013XKtmoR5QCUSTMjiQ3os49

Author: claude