Remove EUROMOD comparator facts from Belgium targets

[MaxGhenis]

Summary

• remove the JRC/EUROMOD-BE comparator source package that was included in Add Belgium target source packages #72
• remove the EUROMOD alias, comparator regression test, source artifacts, and bundle coverage rows
• keep the Belgium target set to the six primary publisher streams from Statbel/SPF Finances/ONSS/ONEM-RVA/NBB

Facts

• Belgium Ledger coverage is now 587 facts across the six primary-source streams
• EUROMOD/JRC comparator rows are excluded because Ledger facts should come from primary government/statistical publishers

Verification

• uv run pytest -q tests/test_belgium_targets.py tests/test_ledger_source_package.py
• uv run pytest -q tests/test_ledger_bundle.py::test_build_bundle_writes_merged_consumer_contract
• uv run ruff check
• git diff --check origin/main...HEAD

Refs #69