It enables to remove "duplicated" line in pip-swh-packages output.
$ ./bin/pip-swh-packages -e swh-core -e swh-model -e swh-core[db,http] -e swh-objstorage -e swh-storage -e swh-scheduler -e swh-journal -e swh-loader-core -e swh-indexer -e swh-search -e swh-vault -e swh-deposit -e swh-core[http,db] -e swh-graph -e swh-lister -e swh-loader-git -e swh-loader-mercurial -e swh-loader-svn -e swh-objstorage-replayer -e swh-scanner -e swh-web -e swh-web-client -e swh-icinga-plugins -e swh-docs -e swh-dataset