Remove obsolete duroxide migration verification from copilot-setup-steps

The verify-duroxide-migrations.sh script was deleted as part of the
BGW-managed migrations work, but the CI step referencing it was not
removed from copilot-setup-steps.yml.

Author: pinodeca

.github/workflows/copilot-setup-steps.yml

@@ -112,6 +112,3 @@ jobs:
       - name: Prefetch Rust dependencies
         run: |
           cargo fetch
-
-      - name: Verify duroxide migrations match upstream
-        run: ./scripts/verify-duroxide-migrations.sh