archivers/zstd: remove lz4, fix manpages

This shortens the requisite path for lang/python314,
and we have a separate archivers/lz4 port.

This also updates the manual pages to v1.5.7, the
release tarball missed updating them, see
https://github.com/facebook/zstd/releases/tag/v1.5.7

PR: 290739
Approved by: maintainer timeout (sunpoet@, 15 days)