lister.core: Remove origin creation from lister behavior

Prior to this commit, lister did create origins as well in the archive (swh-storage's db). Now, we plan to only schedule those origins for ingestion (and we let the loaders do the actual creation).

Test Plan

tox

Then swh-docker-dev through multiple runs.

First run:

• checkout origin/master (without this diff)
• Add dummy/witness new task type loader-gnu (for the listing to actually succeed, implementation detail of the current lister/loader's status)
• Run gnu lister through scheduler
• Check swh-scheduler db (new tasks added)
• Check swh-storage db (new origins)
• Check swh-lister db (filled-in cache)

Second run:

• checkout this diff
• Add dummy/witness new task type loader-gnu
• Run gnu lister through scheduler
• Check swh-scheduler db (new tasks added)
• Check swh-storage db (no new origins as this behavior got removed here so \m/)
• Check swh-lister db (still filled-in cache)

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Migrated from D1579 (view on Phabricator)