Use $item instead of $item['id'] in edd_email_receipt_download_title

In EDD 1.8.x the filter passed `$title`, `$item`, `$item['id']` and `$price_id`. In EDD 1.9 the `$item` was removed.

I'd like to propose we drop `$item['id']` and put `$item` back in seeing as you can access everything from $item like quantity, price, id, etc.