Remove vcf_header option from write_vcf

[jeromekelleher]

vcztools view needs to produce the appropriate header in all situations, and having an input header as an option is not really very helpful. We need to subset the samples and fields in all sorts of ways, and parsing the source header here is not the right approach. Header parsing should be done in bio2zarr.

Note that do this fully, we will need to update the VCF Zarr specification and vcf2zarr in order to store sufficient information about the header, rather than the header itself. This will require some coordinated updates across repos.

I think the simplest approach here is to just delete the option for proving a complete header here, and see what we're missing.

See:

• Clarify purpose of the vcf_header attribute and/or refine? vcf-zarr-spec#15

[jeromekelleher]

See the linked issues in sgkit-dev/vcf-zarr-spec#15 (comment) for notes on how we might avoid storing the full header, and retain lossless encoding of the information in it.