[tz] The link-name, America/Virgin, is linked to two zones in 'backzone'

[Yan-Jie Wang]

A link-name (the second column of the Link line) in a file should be
unique.  However, 'America/Virgin' is linked to two zones
(America/Port_of_Spain and America/St_Thomas) in 'backzone'.

The error is in the latest commit as well as in the archive tzdata2021e.tar.gz.

The link to the file:
https://github.com/eggert/tz/blob/6c15079/backzone

Yan-Jie Wang