kojira: check rm queue before adding new path
    
    It is a remnant of previsou unification of rmtree paths. Instead of
    deleting tree directly while deleting repo it is put into queue now. So,
    other thread looking for expired/deleted repos can find it also and add
    it twice. Internal rmtree can check the queue before adding duplicate
    path. As a side-effect manager.rmtree can also never fail, so try/except
    can be removed from there.
    
    Fixes: https://pagure.io/koji/issue/2716