[syncschema] don't arbitrarily remove constraints from the in-memory schema For some constraint types, it may make sense to have several constraints of that type simultaneously. In such a case, removing one of them from the in-memory schema is wrong. Closes #7446353

usr/lib/python2*/*-packages/cubicweb/entities/
usr/lib/python2*/*-packages/cubicweb/ext/
usr/share/cubicweb/cubes/
usr/lib/python2*/*-packages/cubicweb/*.py