vcf_filter script - pkg_resources is deprecated

[davmlaw]

If you run vcf_filter.py

You get:

$ vcf_filter.py
/home/dlawrence/localwork/variantgrid/.venv_django5/bin/vcf_filter.py:4: UserWarning: pkg_resources is deprecated as an API. See https://setuptools.pypa.io/en/latest/pkg_resources.html. The pkg_resources package is slated for removal as early as 2025-11-30. Refrain from using this package or pin to Setuptools<81.
  import pkg_resources

See https://setuptools.pypa.io/en/latest/pkg_resources.html