patches: Update ZFS enablement patches

Replace

  debian/Set-defaults-for-zfs-tools.patch

with

  backport/meson-Enable-ZFS-storage-backend-even-more-often.patch
  backport/meson-Stop-looking-up-ZFS-programs-at-build-time.patch

Thanks to recent upstream changes, we no longer need to carry
downstream changes in order to enable ZFS support without making
it a build time dependency.