Update to build without base-0

Update to build without base-0

NOTE: the overlapping readme/license files from tzdata/tzcode are identical

Also, note the GMT files are now 0 byte:

  2020a.old/usr/share/zoneinfo/Greenwich
  2020a.new/usr/share/zoneinfo/Greenwich

But as zdump behaves identical, the change is probably okay:

$ zdump -v 2020a.old/Greenwich
2020a.old/Greenwich  -9223372036854775808 = NULL
2020a.old/Greenwich  -9223372036854689408 = NULL
2020a.old/Greenwich  9223372036854689407 = NULL
2020a.old/Greenwich  9223372036854775807 = NULL

$ zdump -v 2020a.new/Greenwich
2020a.new/Greenwich  -9223372036854775808 = NULL
2020a.new/Greenwich  -9223372036854689408 = NULL
2020a.new/Greenwich  9223372036854689407 = NULL
2020a.new/Greenwich  9223372036854775807 = NULL