Update openindiana-download-mirrors.md

Japanese mirror by Tsukuba no longer provides a mirror of OI. Remove it from the list.

Author: microchip8

docs/handbook/openindiana-download-mirrors.md

@@ -36,5 +36,4 @@ List of DLC Mirrors
 [ftp.nluug.nl/pub/os/openindiana.org](https://ftp.nluug.nl/pub/os/openindiana.org/)   | HTTPS/FTP | Ede, Netherlands    | 1Gbit/s      | NLUUG                                   | [nluug.nl](https://www.nluug.nl/)                         | Up to date
 [mirror.math.princeton.edu/pub/openindiana](https://mirror.math.princeton.edu/pub/openindiana) <br> [mirror.math.princeton.edu/pub/openindiana-iso](https://mirror.math.princeton.edu/pub/openindiana-iso/) | HTTPS | Princeton, NJ (USA)    | 1Gbit/s | Princeton University | [princeton.edu](https://www.princeton.edu/) | Up to date
 [openindiana.teambelgium.net/oi/](https://openindiana.teambelgium.net/oi/)                         | HTTPS/RSYNC | Leuven, Belgium        | 500Mbit/s      | Team Belgium                     | [openindiana.teambelgium.net](https://openindiana.teambelgium.net/) | Up to date
-[ftp.tsukuba.wide.ad.jp/illumos/openindiana](https://ftp.tsukuba.wide.ad.jp/illumos/openindiana/) | HTTPS | Tsukuba, Japan | 1Gbit/s   | Tsukuba WIDE Public Mirror service      | [tsukuba.wide.ad.jp](https://ftp.tsukuba.wide.ad.jp/)     | Last updated 2021
 [ftp.gtlib.gatech.edu/pub/OpenIndiana](http://ftp.gtlib.gatech.edu/pub/OpenIndiana/)  | HTTP/FTP  | Atlanta, GA (USA)   | 1Gbit/s      | Georgia Institute of Technology         | [gatech.edu](https://www.gatech.edu/)                     | Last updated 2021