Drop us-data package from bundle scaffold

[anth-volk]

Fixes #432

Summary

This removes policyengine-us-data from the current certified bundle package scaffold now that the certified US dataset is represented through the Populace data release manifest path rather than the legacy Python data package.

Changes included:

• Remove policyengine-us-data from src/policyengine/data/bundle/manifest.json package metadata.
• Remove the --us-data package update input from the bundle maintenance scripts and docs.
• Update bundle tests to assert US installs only include policyengine, policyengine-core, and policyengine-us.
• Regenerate bundled TRACE TRO manifest and composition hashes for the updated manifest.
• Add a changelog fragment.

Validation

• ruff format scripts/bundle.py scripts/prepare_package_bundle_update.py tests/test_bundle.py tests/test_bundle_metadata.py
• ruff check scripts/bundle.py scripts/prepare_package_bundle_update.py tests/test_bundle.py tests/test_bundle_metadata.py
• python scripts/bundle.py check
• POLICYENGINE_SKIP_COUNTRY_IMPORTS=1 .venv/bin/python -m pytest tests/test_bundle.py tests/test_bundle_metadata.py
• python scripts/export_bundle_release_assets.py --dist-dir /tmp/policyengine-bundle-assets-check

The exported bundle constraints now contain only policyengine, policyengine-core, policyengine-uk, and policyengine-us.