[hooks/syncschema] do not crash on double removal of a constraint Some complicated migrations may entail a double constraint removal. It is not yet known whether this is a genuine cw bug or the result of a complicated migration story, but we should nevertheless not crash. Rather, emit a CRITICAL warning and proceed. Closes #3595309.

missing-dep-for-interpreter make => make | build-essential | dpkg-dev (usr/share/pyshared/cubicweb/skeleton/debian/rules.tmpl)