[web] Do not try to rmtree symlinks in rmtreecontent()
There is a symlink in data directory (created by generate_static_dir() method)
and trying to rmtree() it will fail with an OSError. So we unlink() it
instead.
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