Refactor the sphinx-dev build environment to get rid of the link-stamp step
by installing swh packages in standard (non-editable) mode, so we have an easy to specify swh/ directory in which all the swh packages are installed.
The main drawback of this solution is we loose the possibility of rebuilding the doc (in tox) while editing a package's documentation without rebuilding the tox env (i.e. using tox -r). But IMHO this usage has never been adpoted by anyone, so it's much simpler that way.
Migrated from D3073 (view on Phabricator)