index.json: 404 on https://w3c.github.io/sdw-sosa-ssn/ssn-extensions/

[vmpstr]

I'm not sure how this URL is generated (it's not directly in specs.json only in index.json), but it seems to be 404.

[tidoust]

The URL comes from the W3C API: https://api.w3.org/specifications/vocab-ssn-ext

The W3C API has that URL because... I asked @deniak to update the URL in #1954 (comment) because the previous URL was no longer the latest Editor's Draft.

The URL used to work. That's also the URL advertized in the README of the underlying repository, and what the main repository also claims. But it seems the related folder was dropped as part of w3c/sdw-sosa-ssn#366

I'm not sure I understand what the Spatial Data on the Web is doing here and where the latest version of the Editor's Draft is meant to be.