docs: Fix redondant extlink link warnings on archive.s.o

This should help in fixing the main swh-docs build and the current swh-web-client master build [1]

• [1] https://jenkins.softwareheritage.org/view/swh-draft/job/DWCLI/job/tests/750/console

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Migrated from D6973 (view on Phabricator)