symmetric relations: replace bogus rql2sql translation by a hook The hook ensures X r Y => Y r X iff r is symmetric. The rql-no-hook data importer receives a small amendment but note that: * there exist no test for it * its actual semantics are undefined Hence we cannot prove this hunk breaks nothing, because we cannot prove anything. Closes #3259713.

if not rql('CWConstraintType X WHERE X name "RQLUniqueConstraint"',
           ask_confirm=False):
    rql('INSERT CWConstraintType X: X name "RQLUniqueConstraint"',
        ask_confirm=False)