tests: Simplify svn loading tasks creation tests implementation
Use helper fixture loading_task_creation_for_listed_origin_test from swh-loader-core and remove redundant tests.
Migrated from D8699 (view on Phabricator)
Staging instance, all changes can be removed at any time
Use helper fixture loading_task_creation_for_listed_origin_test from swh-loader-core and remove redundant tests.
Migrated from D8699 (view on Phabricator)