Extract germline calls for the given sample, if tumor only.

def extract(data, items, out_dir=None):
    """Extract germline calls for the given sample, if tumor only.
    """
    if vcfutils.get_paired_phenotype(data):
        if len(items) == 1:
            germline_vcf = _remove_prioritization(data["vrn_file"], data, out_dir)
            germline_vcf = vcfutils.bgzip_and_index(germline_vcf, data["config"])
            data["vrn_file_plus"] = {"germline": germline_vcf}
    return data