deposit: Remove 'negative_utc' from test data
swh-deposit v0.17.0 removes it, to match the removal from swh-model v5.0.0
Migrated from D6935 (view on Phabricator)
swh-deposit v0.17.0 removes it, to match the removal from swh-model v5.0.0
Migrated from D6935 (view on Phabricator)