Remove `main.tasks.scrape_interval_task` if it's not used anywhere

[igorsimb]

main.tasks.scrape_interval_task is legacy code that seems to only be used in tests now.

It has now been replaced with: update_or_create_items_task that contains scrape_items_from_skus + update_or_create_items_interval (which used to be paerts of scrape_interval_task task).

• Check occurrences in code to see if it's safe to delete
• Check occurrences in tests
• Re-write tests to use update_or_create_items_task