[pkg] Tidy substvars usage in control file The documentation package was missing a Built-Using field to record the provenance of the templates. Empty packages or meta packages do not require Depends on a specific Python version, so we can remove the relevant substvars.

missing-dep-for-interpreter make => make | build-essential | dpkg-dev (usr/*/cubicweb/skeleton/debian/rules)
embedded-javascript-library usr/share/cubicweb/cubes/shared/data/jquery.js