Sia Decentrilized Cloud (sic) is listed but not available

[v2.1.0.119_canary_2025-05-29](https://github.com/duplicati/duplicati/releases/tag/v2.1.0.119_canary_2025-05-29)

> Removed the Sia backend as the current implementation is not compatible with the pending hard-fork.

2.1.0.119

[Remove Sia backend #6287](https://github.com/duplicati/duplicati/pull/6287)