jobs/swh-docs: Remove user and sysadmin doc uploads

The SWH documentations have been merged and are now built by a single sphinx-build process so only a single build directory needs to be uploaded from now on.

The documentation will be published at https://docs.softwareheritage.org/sphinx/, this would require to change the redirect from https://docs.softwareheritage.org/ to that new URL, unless we want to directly publish it at the root of the HTTP server.

Related to swh/devel/swh-docs!302 (merged)