biology/htslib: Update to 1.21

Packaged in wip by J Bacon

# pkgsrc-specific changes:

Remove mysterious CONFIGURE_ENV.NetBSD+= hts_cv_have_neon=no.
A comment was added stating that it caused build failures.

# Upstream changes:

Numerous bug fixes and enhancements since 1.17.
Changes: https://github.com/samtools/htslib/releases
