hg: Update for swh.loader.core 3.0.0 and remove initialization boilerplate
Test Plan
will fail because it depends on swh-loader-core!283 (closed) being released
Migrated from D7613 (view on Phabricator)
will fail because it depends on swh-loader-core!283 (closed) being released
Migrated from D7613 (view on Phabricator)