currently for every node we were additionaly loading constraints from
parent node, merging them and then deleting
it makes more sense just to keep already loaded constraints from parent node

Change-Id: I3fcd669547f24eeeac0b77876950ff7436bd5cb3
Reviewed-on: https://gerrit.libreoffice.org/73116
Tested-by: Jenkins
Reviewed-by: Miklos Vajna <vmiklos@collabora.com>