misc/zoneinfo: Updated to 2021b

Briefly:
  Jordan now starts DST on February's last Thursday.
  Samoa no longer observes DST.
  Merge more location-based Zones whose timestamps agree since 1970.
  Move some backward-compatibility links to 'backward'.
  Rename Pacific/Enderbury to Pacific/Kanton.
  Correct many pre-1993 transitions in Malawi, Portugal, etc.